That's accounted for with the development trait.
It's a three-level system, three factors determine how much XP a player gets from Training:
- drill result (gold / silver / bronze medal; the better the medal, the more XP every player earns)
- depth chart position (this simulates the concept of your first-team players getting more reps in practice than your second- and third-team players)
- development trait (after being stratified by depth chart position, players with a better development trait will earn more XP)