If that's the case why do teams even bother with coaching staffs? Why hire an OL coach if he's not going to have an impact on the development of the players he's coaching? Are you telling me Aaron Rodgers becomes virtually the same player today whether it was Mike McCarthy or Steve Spurrier coaching him? Maybe he does, maybe he doesn't. But that's something that other factors like player potential also have a role in.
Also, how does giving players certain bonuses reflect any bit of coaching that has been imparted on the player? So a player becomes more aware thanks to his coach but if he changes teams he forgets everything that went into making him more aware?
And your last line sounds a lot like game prep and progressing players with XP.