I guess you're right in saying that training is not entirely related to competitive games.
I guess you could link training efficiency with game-shape, to give an incentive for managers to play their rookies during competitive matches.
I don't like the idea of being able to train efficiently without giving playing time. Practice is one thing, but competition is a lot more important in a player's development. It's easy to knock down 40% from 3pt range with a some practice, another thing is to stay consistent for 35+ minutes in front of a crowd, against real opposition, and having to play on tough defense at the same time, while trying to avoid picking up you 3rd foul because you have to stay in a rhythm.
"Air is beautiful, yet you cannot see it. It's soft, yet you cannot touch it. Air is a little like my brain." - Jean-Claude Van Damme