And again, the combination of two of my suggestions will do the work, like they do in the NBA.
Players in higher leagues should be more "mature' players, but with lower potentail or with lower rate of improvement.
By that - they're payroll will be high enough to take care of them, and you will need to invest more on their training managing, and on the draft managing. Summary - invest more time on BB-managing.
Crap player exists also on NBA draft.
so you draft useles player, and training is also useless but you had to pay the salary. Nothing of them is reality in the NBA like you say, cause NBA team also trade their draft picks, and draftet players. Also training should be possible like in lower league with the same circumstances etc.
If that what you will decide to do, that what you will get.
If you will decide to invest in the draft for getting better players, and then train them, you will get that.
And like in the NBA, you can make great scouting and come up with a flop instead of the realy good player that will be drafted afterwards.