It’s correct that the Buddha mainly uses reduction in suffering as the way to approach nibbana, this is illustrated in the four stages of holiness being a progressive removal of the fetters. Also in the four noble truths, suffering is the first truth, rather than the cause of suffering, and impermanence is not mentioned, even though it is defined as the cause of suffering (anicca, dukkha, anatta) in many suttas (SN 22.59). The reason the emphasis is placed on suffering is as a teaching strategy, suffering being readily identified with by all listeners. Also reduction in suffering becomes a more observable result of the path compared with mental seclusion, which requires mindfulness of mind states to discern.
However nibbana is also approached from its positive aspect, and the recollection of nibbana is the last of the ten recollections in the forty subjects of meditation. So direct contemplation of the peace of nibbana is encouraged. Not so obvious is the link between mental seclusion and nibbana, were it constitutes the first experience of detachment from samsara. This is the origin of the instruction to “subdue greed and distress with reference to the world” in the introduction to the Satipatthana sutta, and the subsequent repeated statement “he remains independent, not clinging to anything in the world” throughout the body of the sutta. This indicates a progressive non-attachment to samsara, which invariably means the mind is turning towards nibbana. The fact that nibbana is glimpsed in stream entry means that its acquisition is gradual (SN 12.68), so there is equally a positive pathway to nibbana described. The practitioner has to develop a conceptual and in the above terms, experiential knowledge of nibbana as an alternative destination when detachment begins to be occur.
The Buddha’s truth is superior in terms of reliability. Some levels of attainments are described as "supramundane"which shows the superior nature the Buddhist approach to knowledge/truth.
If you think in terms of the realm of all possibilities, the Buddha chose to frame what he knew with emphasis on suffering.
The emphasis on suffering cannot be understood without it being a path to attain knowledge, otherwise, it would be a mere obsession. A mere obsession about suffering would be pathological, just think of a germophobe for instance. Or if you raise the hypothetical question: why we are here? not to suffer does not make much sense.
Accordingly, having suffering as an entry point seem to be purposive. Other religions attempted to provide answers as to why suffering is necessary such as Christianity through the idea of original sin in which suffering is a way to cleanse ourselves, but such explanations are nonsensical from a Buddhist perspective. From a Buddhist perspective, as i understand it, suffering is not necessary, and yet, it seems necessary entry point to bring things to conclusions, or to reach certainty.
Why suffering has to be the entry point or the gateway to the ultimate? is it a mere coincidence? is it the nature of things? is it the Buddha’s bias when he investigated suffering and stumbled upon the highest form of knowledge by sheer luck? or is there an explanation that can be understood by the mind?
Because suffering is a state of mind that is difficult to be delusional about.
When you’re suffering, there’s an immediacy to it: you know you’re suffering. And there’s an urgency too: you are motivated to find a way out — an escape from your pain.
These two aspects, clear comprehension and motivation (together with mindfulness) form the very core of the enlightenment factors. Or, in the Buddha’s own words:
Just as one whose clothes or head had caught fire would put forth extraordinary desire, effort, zeal, enthusiasm, indefatigability, mindfulness, and clear comprehension to extinguish the fire on his clothes or head, so too that bhikkhu should put forth extraordinary desire, effort, zeal, enthusiasm, indefatigability, mindfulness, and clear comprehension to abandon … unwholesome qualities.
~ SuttaCentral
Thank you Venerable 
Interpreting things/reducing them to suffering seem to be an effective way of investigating things and hopefully seeing them as they are. It seems to appeal to us and to catch our attention, but acknowledging it as a method might help us avoid its excesses? There seem to be more to life than suffering. If ending suffering is all what we want or worth living for, we would envy stones, but we don’t.
One might be tempted to focus on delight as “more to life,” yet in MN1 the Buddha tells us quite starkly:
delight is the root of suffering
And this statement brings us to a complete stop, leading us to consider impermanence. Because if delight is the root of suffering, then our pursuit of delight is merely the incessant pursuit of suffering. We chase our tails furiously, looking for the delight to end all delights. Yet all we find is suffering.
But if suffering is born, it must also die.
If we are born, then we too must die.
Understanding this, we relinquish the impermanent as unsatisfactory to walk the Noble Eightfold Path.
This is similar to Uggāhamāna’s argument in MN78, where he refers to a baby:
When an individual has four qualities I describe them, not as an invincible ascetic—accomplished in the skillful, excelling in the skillful, attained to the highest attainment—but as having achieved the same level as a little baby. What four? It’s when they do no bad deeds with their body; speak no bad words; think no bad thoughts; and don’t earn a living by bad livelihood. When an individual has these four qualities I describe them, not as an invincible ascetic, but as having achieved the same level as a little baby.
The Buddha then goes on to explain further:
When an individual has ten qualities, master builder, I describe them as an invincible ascetic—accomplished in the skillful, excelling in the skillful, attained to the highest attainment.
Specifically the highest attainment we should wish for is:
right view, right thought, right speech, right action, right livelihood, right effort, right mindfulness, right immersion, right knowledge, and right freedom
What “excesses” do you imagine, exactly?
Funnily enough, my first meditation teacher called meditators he admired “statues” as a term of praise when describing their stoic, perfect stillness in meditation.
It is potentially excessive because it reduces everything to suffering when in fact it does not have to be the case. Take the Loka sutta as an example where the Buddha reduced the “world” to whatever is experienced through the six senses.
If we interpret the Loka sutta literally, then Buddhism would be a form of solipsism. If Buddhism is not solipsism, then the Buddha reduced the world to the six senses for a purpose in which this view of the world is probably a beneficial metaphor that is not ultimately true.
In light of the above, why the emphasis on suffering is not a useful metaphor? We live in a world where most people don’t interpret everything in terms of “suffering”, so would acknowledging it to be an interpretation be useful? would the question “why suffering as an entry point” be a legitimate one?
One might be tempted to focus on delight as “more to life,” yet in MN1 the Buddha tells us quite starkly:
delight is the root of suffering
And this statement brings us to a complete stop, leading us to consider impermanence. Because if delight is the root of suffering, then our pursuit of delight is merely the incessant pursuit of suffering. We chase our tails furiously, looking for the delight to end all delights. Yet all we find is suffering.
But if suffering is born, it must also die.
If we are born, then we too must die.
Understanding this, we relinquish the impermanent as unsatisfactory to walk the Noble Eightfold Path.
Indeed. Not all forms of delight are treated equally:
“These, Bhante, are the eight astounding and amazing qualities that the asuras see in the great ocean because of which they take delight in it. But do the bhikkhus take delight in this Dhamma and discipline?”
“Pahārāda, the bhikkhus do take delight in this Dhamma and discipline.”
Delight as a root cause of suffering is not easy to comprehend in my case and i guess has to do with the deceptive nature of samsara, not as a pessimistic view of things.
Everything else being equal, if i have to choose between an open and joyful temperament or a dark and gloomy one, i would go for the former every single time.
In an expanded version of dependent origination in Upanisa Sutta (SN 12.23), the Buddha showed suffering to be the proximate cause of further links leading to liberation:
Just as, monks, when rain descends heavily upon some mountaintop, the water flows down along with the slope, and fills the clefts, gullies, and creeks; these being filled fill up the pools; these being filled fill up the ponds; these being filled fill up the streams; these being filled fill up the rivers; and the rivers being filled fill up the great ocean — in the same way, monks, ignorance is the supporting condition for kamma formations, kamma formations are the supporting condition for consciousness, consciousness is the supporting condition for mentality-materiality, mentality-materiality is the supporting condition for the sixfold sense base, the sixfold sense base is the supporting condition for contact, contact is the supporting condition for feeling, feeling is the supporting condition for craving, craving is the supporting condition for clinging, clinging is the supporting condition for existence, existence is the supporting condition for birth, birth is the supporting condition for suffering, suffering is the supporting condition for faith, faith is the supporting condition for joy, joy is the supporting condition for rapture, rapture is the supporting condition for tranquillity, tranquillity is the supporting condition for happiness, happiness is the supporting condition for concentration, concentration is the supporting condition for the knowledge and vision of things as they really are, the knowledge and vision of things as they really are is the supporting condition for disenchantment, disenchantment is the supporting condition for dispassion, dispassion is the supporting condition for emancipation, and emancipation is the supporting condition for the knowledge of the destruction (of the cankers).
I used a 1995 accesstoinsight version by Ven. Bodhi instead of SC because SC abbreviated it too heavily.
In this version he translated the relationship between the links as the supporting condition, but he later (2000) favored Ven. Thanissaro’s phrase proximate cause, that is, dukkha is the proximate cause of saddha and the rest. According to my notes another translator went with prerequisite. Bhante Sujato gives dukkha as a vital condition leading towards liberation.
Hence, suffering can be seen as the necessary starting point for liberation.
[Edited to improve wording.]
More on the pivotal role of suffering. From AN 6.63 Nibbedhikasutta (Penetrative):
'Suffering should be known. The cause of suffering should be known. The diversity in suffering should be known. The result of suffering should be known. The cessation of suffering should be known. The path of practice for the cessation of suffering should be known.’ Thus it has been said. In reference to what was it said?
. . .
And what is the result of suffering? There are some cases in which a person overcome with pain, his mind exhausted, grieves, mourns, laments, beats his breast, and becomes bewildered. Or one overcome with pain, his mind exhausted, comes to search outside, 'Who knows a way or two to stop this pain?’ I tell you, monks, that suffering results either in bewilderment or in search. This is called the result of suffering.
. . .
Now when a disciple of the noble ones discerns suffering in this way, the cause of suffering in this way, the diversity of suffering in this way, the result of suffering in this way, the cessation of suffering in this way, and the path of practice leading to the cessation of suffering in this way, then he discerns this penetrative holy life as the cessation of suffering.
The bolded phrase is found here in Bhante Sujato’s translation.
This entire Sutta, by the way, would probably be my “desert island” sutta!
Very nicely stated, thank you. 
Thank you Venerable 
Suffering being the condition for searching, the universality of suffering among living beings, and the idea of endless rebirth until true knowledge is attained, all of this give the impression that our existence (suffering) is somehow justified, which is a hindrance to liberation!
How to reconcile the above?
There’s nothing noble or ennobling about suffering. But starting to comprehend it opens up the path.
Ah! I see! You’re falling into the trap of equating phenomenology with solipsism.
Indeed you’re right that the potentially solipsistic Loka sutta needs to be balanced with (mundane) right view, specifically:
…there is mother and father; there are beings who are reborn spontaneously…
~ MN 117 (BB trns)
So, you see, the Buddha wasn’t trying to deny the existence of other beings when he encouraged us to consider that we can only experience those other beings through the six “doors” of our senses.
Thank you Venerable
The example i provided about the Loka sutta was meant to show how reducing everything to “suffering” can be excessive. I was not equating phenomenology with solipsism.
To put differently: what would constitutes the “wrong grasp” of the first noble truth?
Idk! What do you think?
Not easy to answer. I can think of some benefits of such approach. The act of reduction has a unifying effect same as any theory with explanatory power. Constructing an argument that focuses on reliability (or lack of) can be a driver for a search for a more reliable knowledge.
On the other hand, all theories are excessive in the sense that their validity relies on negating all other interpretations. Using impermanence as a basis for an argument is akin to shooting oneself in the foot due to the paradoxical nature of the term. Impermanence can be used to justify about anything!
Sure. The Buddha is instructing us to view reality at a particular angle: from the perspective of non-contention
But privileging one perspective (right view) to the exclusion of other perspectives is not necessarily “excess.”
I would call working jobs we hate so we can buy s*** we don’t need “excess.” I would call destroying the planet so people in moderately warm climates can have AC “excessive.” I would call protesting greater racial equity by electing “populist” white mobsters “excessive.”
In short, I would call greed, hatred and delusion “excessive.”
But there’s nothing “excessive” about the middle way. 
Well, there’s a reason why not even in the most audacious Buddhist sects, no one speaks of “unconditioned dharmas of the path.” AFAIK, the path is absolutely never the unconditioned in some mystical way. People sometimes speak of “pure dharmas of the path,” but I don’t know if that is EBT language or not, tbh, (which would make an interesting side-discussion in a different thread perhaps) and that language is chosen specifically to avoid “unconditioned dharmas of the path.”
IMO this is a basic Parable of the Raft situation. Perhaps the Raft is assembled from the provisional dharmas of the proverbial stormy sea of saṁsāra, as opposed to “assembled of” the unconditioned dharma(s) of the shore of nirvāṇa, whatever that would mean. The Parable of the Raft is a basic “the path is not the goal” scenario. Because the path is not the goal, the path can be “of suffering,” so to speak. If the Path/Raft is a vital “gateway” of sorts (I am trying to use the language from the title of your thread here), which, without seeing it, navigation can be treacherous and, without entering through it, safety unlikely, then, because it is not the Goal/Shore, it too can be suffering.
IMO.
The raft simile can be interpreted as “the path is not the goal”, or as replacing an ontological mindset (things exist or do not exist) with a pragmatic one (use things skillfully, without attachment). By definition, those who reached the other shore are not in need of such simile. The simile is useful only to those who need it, i.e those who are constructing the raft and trying to reach the other shore.
What i am trying to say is that the relationship between the path and the goal does not seem to be as linear as presented in your post. The act of reduction is extended to the goal “the end of suffering”. The intertwined nature of the four noble truths makes the path begins with right view (which includes knowledge of the third noble truth), Same thing applies to DO where the root cause is presented as “ignorance”, which can be defined as not knowing the four noble truths and/or the three marks of existence.
In light of the above, the duality of the path and the goal (as extremes) and the act of negotiation between the two can be seen as another useful presentation aiming at discovering the middle way, or right grasp, or certainty or whatever we want to call it.
When we think that the path is no longer needed when the goal is reached, same game of language can be extended to the goal: is the goal needed when the goal is reached? When the duality serves its purpose, both seem to be no longer needed.
If the four noble truths are approached as “useful presentation” then contemplating why this presentation can be the basis of an interesting discussion.