Some players progress and reach their potentials others do not. Playing time, coaching factor into the formula. I do not believe that if the same player is allowed to kill stat wise at aa he will in fact be a better player than if he played the same amount at a ML level. It makes much more since that a player playing the same amount would in fact benefit from better coaching unless coaching has zero impact. I have players who progressed in the majors very well as very young starters and I have players who failed to progress in the minors.