One possible solution could be to remove training positions, but introduce penalties on certain skills in combination with skill levels.
Let's say I want to increase one of my players passing, which is absolute 0. In such a case, I think we should be able to get 100% regardless position.
If, on the other hand, I want to train a guy who is pretty solid in passing (like 15), it would require him to play PG to get 100%.
This could be pretty complicated for all the skill-position, age, height, whatever constellations, though.
But IMO we should start by changing the pace of training depending on skill level. Training from 0-1 should not be the same as going from 19-20
Größter Knecht aller Zeiten aka His Excellency aka President for Life aka Field Marshal Al Hadji aka Lord of All the Beasts of the Earth and Fishes of the Seas aka aka Conqueror of the Buzzerbeater Empire in Europe in General and Austria in Particular