How best to develop a player.

[Amane Ito]

From my experience, a bust player (who always give 6 or below form) can take up to two seasons to recover.

I keep them on purpose, never had any bust that won't bounce back 2 years later (that yield 7~8 average rating) while keeping them benched.
Some of my best players were once busts. I suspect it is the stats value that can be lined up good or bad, so once a player is in excellent shape I stop using sp on him and just let unused sp pile up.

But, this is a lot to train and a lot of friendly to play...