I'm inclined to agree with you that I'm more likely at the Three Characteristics stage, which is obviously a slightly uncomfortable thing to have to admit but also a relief.
It's great that you're able to do this, the ability be honest with yourself is essential and will stand you in good stead. Look at what it is that seems to feel discomfort at the idea of not having 'got' something or somewhere, the sensations that make up that feeling can be very informative.
And because of it I think I'll now make the most of being below the A&P and focus on samatha until I can vipassanize with relative ease. Tbh, returning to vipassana over the past few days had begun to remind me of the slightly traumatizing 10-day Goenka retreat I did where I worked exceptionally hard but didn't really improve much at the technique at all (despite gaining some insights all the same) - I don't think I have the patience for the pace I seem to naturally improve at.
Do whatever works for you, finding a good balance between samatha and vipassana, e.g. doing 30 minutes of concentration followed by 30 minutes exclusively doing insight practice, will help strengthen your practice. Developing that mental stability is always good and can be really useful when you're feeling a bit raw or drained, but experiential insight into the true nature of things is what leads to progress.
If you're noticing those same unpleasant sensations as you noticed while on retreat, don't try to avoid them or change them, they're just side-effects of the process and should be treated the same as any other sensation: Investigate them as bare sensation, and don't get caught up in the content, emotionally or psychologically, or be pulled to and fro by memories of what happened before.
Your points about over-analyzing while meditating and over-eagerness to make things happen are also spot-on. Uncannily so! Did I even give you enough information to draw such accurate conclusions??
One of the good things about this site is that most of us have been pretty hardcore meditators for a long time and have learned a million ways
not to make progress.

Whether it's thinking you're completely enlightened, or mistaking one ñana for another, we've all fucked up along the way at some point and, due to that, it makes it easier to see when someone else is doing something which, from your own experience, you know doesn't help practice in any way.
Your point about not even trying to induce pleasurable sensations seems to contradict the advice of other members of this site though, and Leigh Brasington.
I was using "induce" in the sense of consciously trying to cause those sensation to arise, but I can see how that could have been misinterpreted. Simply staying with the breath as consistently as possible is what induces those pleasurable sensations, I was trying to point out that there's no conscious effort on your part to cause this to happen. I've written an article
here which might help a bit, and hopefully clarify some of the practical aspects somewhat.
I think in future I'll try to ensure my attempt at appreciating the 'beautiful breath' is just a very subtle and barely conscious one, but waiting for the mind to notice it on its own seems to be crossing into hard jhana territory and something I don't think I have the time to invest in doing.
Recognize that breathing just happens, how you don't actually need to anything to cause breathing to happen and how any ideas that you do are just that: ideas, thoughts, mental objects with no objective existence. That in itself is miraculous and can cultivate a sense of wonder which is conducive to the arising of piti and sukha, so try openly accepting whatever comes up and just be present.
Any better?