A neural net would be able to read the opposing defense more quickly and accurately than any human, but it would not be a fair fight (the human doesn't get a bird's eye view of things!).
It just doesn't have as big of an impact though. Each team has a very limited set of plays it's actually able to call and execute. Maybe 300 max (as a guess). Many times much less than that. So there's really not much room for an AI to see huge improvements via play calling.
It's really all about execution on the field and the "feel" of the game.
