Arrggh, discussions like this just make me want to meditate! 
But I got feedback even in real life that it’s helpful to people who are confused about the topic, so I’ll stick around here a bit more. And exchanging thoughts on these subjects is also helpful for me, so thanks everybody.
Thanks for those links. 
I will need to look into the venerable Pa Auk’s teachings a bit more one day, although I have to say it is exactly his strong reliance on the Visuddhimagga which has put me off till now. 
As to the article on nimittas, I don’t have any problems with it. I actually agree that in the jhānas there are no lights. In the first jhāna the object is pīti-sukha, not a light or other nimittas. The nimittas are a way into jhanas, but not the jhānas themselves. That is likely one reason that the light nimittas aren’t mentioned super often in the suttas.
Another likely reason the suttas don’t often mention them is that the mind can represent itself in many ways to meditators. Lights are a common way, but they’re not a requisite. Nimittas can also be “sounds” or certain “bodily feelings” or metta or what have you. But these “sounds” aren’t heard by the ear, nor are the “bodily feelings” felt by the body: they’re all just representations (or reflections or “signs”) of the mind. Many people find it hard to describe this territory of meditation. This diversity in hard-to-describe experiences can also explain why the suttas don’t tend to pin themselves down to lights and forms alone. Notice also that the instructions in MN128 are given to three specific bhikkhus, not to the general populace like most other texts on meditation. The three experienced lights and forms, but that doesn’t mean everybody always does.
A third reason is that advanced meditators may be able to skip the stage of nimittas altogether. I wouldn’t be surprised if the Buddha for example was able to go straight into jhāna, skipping any kind of lights or other nimittas.
As to the article questioning whether nimitta in MN128 refers to the lights or idiomatically to the ‘cause’ of samādhi, I agree with Ven. Ānalayo in his comparative study of the sutta: “This sense of nimitta as a mental ‘sign’ or object used for the development of concentration would also fit the present context well, which describes meditative visions and the development of concentration. At a later point of its exposition, the Upakkilesa-sutta [MN128] in fact explicitly uses the term nimitta in order to refer to the vision of light and forms that Anuruddha and his companions had been unable to stabilize, a usage where nimitta clearly stands for a mental sign, for something that is perceived.” That is to say, it certainly doesn’t mean “cause” at that later instance, so Ven. Bodhi’s translation “you should understand the cause for that” is perhaps not literal enough, and it should be “you should penetrate that sign [nimitta]”, meaning basically what you said earlier, “absorb oneself in nimitta”, or “enter that nimitta”. (Edit some days later: I’m now more convinced Bodhi’s translation is more likely to be correct.)
Although MN128 is indeed the most explicit text on the nimittas, I don’t think it is alone in describing these experiences. I see references elsewhere too, though they don’t use the word nimitta: both in the Ānāpānassati and Satipaṭṭhāna Suttas, but particularly in the kasinas and “the eight bases of transcendence/mastery”.
First, in the Ānāpānassati Sutta (MN118) it says: “I’ll breathe in experiencing the mind.” This “experiencing the mind” refers in my experience to the same stage of meditation described in MN128. It’s not called a light or form here, because what you are actually experiencing when you “see” (or “hear” or “feel”) a nimitta is the mind itself. This instruction talks about the same thing as MN128, but more directly, bypassing the perception of light and going straight to what the light represents, which is the mind.
To continue, the subsequent instruction in ānāpānassati is “gladdening the mind”, which is the stabilizing of the lights that MN128 talks about. Put simply, it’s because of lacking gladness that the various hindrances take over. If the mind is truly glad, it won’t become sleepy, restless, distracted, and so forth.
Then the next step of Ānāpānassati is “samadhi-ing” the mind, unifying the mind, i.e. moving towards jhānas. In the next step the mind is “liberated”, which means the hindrances are completely abandoned and the mind enters the jhānas. (These two steps essentially go together.) The jhanas are also called temporary liberations of the mind (e.g. MN122), and this is what “liberating the mind” in Ānāpānassati refers to. It can’t mean liberation in the ultimate sense of ending of craving, because there are still contemplations to be done afterwards.
So the Ānāpānassati Sutta fits MN128 very well, in my view.
In the Satipaṭṭhāna Suttas I also see similar ideas to MN128 under the third factor of “mind”. For example, when MN128 mentions “loss of focus on forms” and “perception of diversity” those are examples of “the scattered mind” of the Satipaṭṭhāna Suttas.
Now, I may be opening another 
of 
, but I also think the kasinas (which are not super common in the suttas but also not exactly rare), in later tradition taken to be physical disks, were originally meant to be mental perceptions we now call nimittas. For example, “the meditation on universal yellow” (AN10.25) would be a yellow light which takes up your whole awareness, the “universality” implying among other things that you don’t perceive the body anymore. (Kasina literally means ‘total’, hence Bhante Sujato’s translation “universal”. Perhaps “pervasive” gives a better sense of the meaning.)
The kasinas are not explained in much detail in the suttas, but in MN77 they precede the jhānas, so it seems they lead up to them, as is commonly assumed. Then they fit the lights and forms of MN128 extremely well, with ttese kasinas and nimittas both leading to samādhi. The various color “kasinas” are then the light nimittas (obhāsanimitta) of MN128, and the elemental kasinas (including space) being the form nimittas (rūpanimitta).
Also very tellingly, MN128 concludes the development of these nimittas with: “I perceive limitless (sañjānāmi appamāṇāni) lights and see limitless forms” and the kasinas are likely said to be “perceived as limitless” (sañjānāti appamāṇaṃ). Same words, same ideas. So the kasinas are what MN128 calls nimittas. A yellow kasina is a yellow nimitta, for example.
Another reference to nimittas seems to be the “eight bases for transcendence” (or “eight bases of mastery/overcoming”), for example at DN16, AN10.29. We again have mentions of “forms” and “perceptions”, and the word “limitless” reappears again here for the higher perceptions. The exact same colors as the “kasinas” are mentioned as well. So it’s quite clearly presenting the same idea as the kasinas, and therefore the same as MN128, which also talks about limitless perceptions of forms and lights (i.e. colors). Accordingly, Bhante Sujato notes on these “eight basis” at DN16: “The ‘visions’ (rūpā) seen externally are the lights or other meditation phenomena that today are usually called nimitta." (I’m not exactly sure why the nimittas are said to be “seen externally”, though. The commentaries seems to say it’s because they are opposed to the “internal” form of the body. 
So then it’s external in the sense of being an external āyatana, a sense object, though it’s a mental one.)
In short, the nimittas are in other places too, not just in MN128, just under different names.
I’m well aware that some of these references are somewhat opaque, and I also still have some questions about them (so what I did say is subject to revision 
), but I think they make much more sense in light of the deeper jhanas which require nimittas, compared to the bodily jhanas where this sort of stuff is generally just seen as commentarial ideas that can be disregarded. But all these things are also all found in various parallels, so they clearly predate the commentaries by a long time, as is the case with MN128.
May I ask why you find MN128 “disturbing”? I hope I am not disturbing you even more! 