The thing is, frankly, even 10 years is not sufficient for an average person to become advanced
and age probably works against you
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First of all, I don't think 32 is super old, and especially if you have been learning stuff all your life, you can still learn quite well. I've had friends who started doing their PhDs at that age, and didn't seem to slow down one bit. Even for those who complete their PhDs and become researchers, that's the age where they need to make their mark, and end up working (focusing and "learning") 10-12 hours a day.
You seem to be rather set in your viewpoints. I have responded earlier with the fallacy in your approach, that is, there are a lot of things which a teacher would be able to correct in a few months, which you could have improved upon 8 years ago, but instead charged ahead ignoring. Unless you do that, you can't legitimately lay claim to have exhausted your possibilities.
As someone who has self-taught for a while, there are things you miss, inevitably. There are even things you miss when you study with a teacher! And correcting those things eventually greatly improves various aspects of your playing. It may not be possible to truly understand what exactly is going on in the hand just by looking at videos, because you can only see posture, and it's impossible to see how much weight and energy is going into each stroke. And this is just one example where self-instruction will possibly fail, there are others. And one of those is not realizing when and how you can increase your expected standards. I thought it wouldn't be possible to play everything "perfectly" in one go, but it turns out it is and I've done it once or twice.
As I said, you've liked at research papers and drawn the wrong conclusions imo. For what it's worth, most students who have been playing for 10 years with good teachers can't play true virtuoso material. Is it the students' fault? Perhaps, perhaps not. We can only speculate. However, don't underestimate how much proper effort in a particular direction can get you. If you're seriously trying to reach an advanced level of playing at your instrument, spending a few hours a day is just expected, nothing special. What you need to look at is how every second of your practice can be improved.
I'm speaking from experience. People here have appreciated the fact that you've been able to dedicate 3 hours a day, and it's not bad. However if you truly want to gain an advanced level of playing, that's not what truly matters. You need to set your sights higher. Blind effort does not get you there and many people fail down that path. You keep mentioning 3 hours of effort as if it were exceptional, it really isn't when it comes to piano practice, when you are attempting to play at a high level. Most aspiring piano majors will be practicing more than that.
I say this not to discourage you. But your claim is basically that you haven't been able to get to an advanced level of playing despite putting in an unusually large amount of effort. I'm just saying the latter isn't the case.