I have a few comments:retrofuturist wrote: I'm not saying insight-knowledges, dark nights etc. are fraudulent, and I'm not saying they're not Dhamma... I'm simply saying they're not recorded anywhere as being the Buddha's teaching.
1. Much stuff is rather obvious, though not explicit, in the various suttas and references I gave some time ago, which you don't appear to have addressed.
2. In many cases, where you see "additions" I see the commentaries and the teaching of modern teachers as saying (in short): "In the experience of many, when one applies the Buddha-Dhamma, this is what tends happens". Not an addition, a report of other practitioner's experience. [In contrast to the mis-characterisation one sometimes sees that the commentaries as merely an academic exercise.]
3. Much of the advice in the commentaries (and modern approaches) is not actually claiming to be Dhamma, so is not a "Dhamma Addition", in my opinion. For example, the advice to use breath counting as an introductory exercise, or start with metta towards oneself are just useful, mundane, advice that has been found helpful by experience.
One final point: The suttas recommend getting advice from a local teacher who can admonish the student and, presumably, provide the sort of detail instruction discussed in points 2 and 3 above. The Buddha won't do that for us, unfortunately, so unless we maintain a living tradition that's a crucial piece of sutta advice that we can't take...