[blindluke]

> it was exactly 8.5 hours of focused, deliberate practice

As already pointed out, that's a very low amount of practice to change the technique. For piano, when learning forearm rotation, the point when it became much, much more comfortable to me than my previous way of playing was after roughly two months of practice, 10-12 hours a week. That's just my experience, but when I asked my teacher about not feeling improvements around the one month mark (40 hours in), he said that everything is progressing at an expected rate.