But you have to say that Fisher was responsible for Hermerdinger's hiring, which indirectly credits Fish for any development that took place. If we blame Fisher for his failure with the Rams, then we have to credit him with the success in Nashville.
As for McNair himself, how was he able to become more accurate, when others fail horribly trying to do that? That's inherent ability.
McNair was able to comprehend how to change in reading defenses, another inherent ability. Coaching developed, I guess, what was already there. Maybe the better way to think of this is whether a player is capable of learning and changing when natural ability is not enough?