Exactly. The only person who is unaffected by leadership is the underachiever who wouldn't have reached his potential anyway.
There are too many to count - literally millions - who, despite poor leadership, be it parents, teachers, military officers, whatever, have done quite remarkably, in a good way.
There are also quite literally millions who, despite "great leadership," well, they didn't turn out so well.
I'm not disagreeing with you in entirety; but rather, asking if you intended to broad-brush your remarks, or are you saying that, for better or worse, leadership is the sole contributor to the finished product?
Good quarterbacks are most-often good leaders (at least, during game/practice time) we all get that. In fact, several outstanding quarterbacks would've been better served with quality leadership, which is to say, Coaching, and Management. Peyton's and Eli's papa comes to mind as someone who might have seen some benefit from better leadership; but I'd wager Archie certainly reached his potential, regardless of his Won-Loss numbers.
Again, not trying to argue your point, but question whether it applies as widely, or as generalized as you portrayed it.