I’m coming in here late, but wanted to address the issue you’re expressing, from some translation work I’m engaged in. First, I think you’re right, it’s generally a “turn off” from the message if you tell people that Buddhism says simply all life is “suffering” or “pain”, and honestly I don’t think that’s what the Buddha had in mind.
If you look deeply into the root meaning of dus (duḥ) it seems to indicate something more like “corruption” than bad or evil or pain or suffering or whatnot. For instance, in the Bhagavad Gita there’s a compound “durbuddhi” (dus-buddhi). It is said in regards to the Kurus who are facing Krishna and Arjuna in the war. Are we to understand from this compound that buddhi is suffering, or that buddhi can suffer, or that there is pain in buddhi etc.? I don’t think so. But if we understand it as meaning “a corrupted buddhi” then it makes perfect sense (there are other such examples as well). The Kurus are those who’s buddhi or bodh is corrupted.
So I think we could look at duḥkha and sukha this way:
dus essentially means “corrupt,” and its use as a prefix gives the sense that there is something that is in itself good, but which has been corrupted (like durbuddhi). su essentially means good, and as a suffix gives the sense of something that is in good working order, or as it should be. Or simply put: duḥka is sukha corrupted.
The end of each term, kha, carries the meaning of “hole” and carries two common meanings: 1) the “holes” of the senses (ears, eyes, mouth, etc.), and 2) the hole in the nave of a wheel through which the axis runs. Both of these lend themselves easily to the following interpretation: a kha operating as it should is su-kha, a kha that is corrupted is duḥ-kha. The senses operating as they should be (sukha) don’t necessarily bring what we commonly call “pleasure” or “happiness” (as contrasted with pain or suffering), but rather a kind of ease, comfort, contentment, or even bliss (or our natural, as-we-should-be state). The senses corrupted bring about discomfort, dis-ease, suffering (an abundance of pleasure will bring dis-ease just as an abundance of pain). A wheel with a good axel hole (i.e. well oiled, perfectly round, etc.) makes for a smooth ride (as it should be); a wheel with a corrupted axel (un-oiled, not perfectly round, etc.) makes for a rough ride (“corrupted” or “agitated”).
So, in this interpretation, what we commonly call “pleasure” is often a result of duḥkha, not sukha, and so is “pain”. sukha properly speaking is like a well-oiled machine working as it’s supposed to work and thus leads to a state of ease where neither extreme of pleasure or pain is to be found.
The main point is that both pleasure and pain are “excitements” of the senses (i.e. the sense are in some way agitated), and thus both fall under duḥkha. So, when we tell people that Buddha called life “duḥkha”, it doesn’t come off as so out-of-tune with human experience (which isn’t all suffering) when we understand duḥkha to mean both pleasure and pain. Life consists of a pretty steady alteration of conditions along that spectrum of agitation. If we say: duḥkha is essentially our mind in an agitated state, and sukha is our mind in a calm state of ease (as in the jhanas), I think that brings the idea closer to what we find elsewhere in Buddhist teachings. It’s that agitation that we ought to seek to calm down, through meditation and mindfulness etc. etc. It’s not the simplistic idea that “all life is suffering”. Rather: life (on this earth, in these bodies) is experienced as a constant state of agitation of the senses and mind. Sukha is what we want instead.
But, when we go deeper in regards to sukha we should also say: even sukha is but a conditioned mental state, which must not be grasped onto, but transcended in the higher states of jhana.