the guys that succeed at the pro level - they work their asses off.
Manziel hasn't worked all that much in college. He did well, he's talented. So was Tebow.
But is Manziel going to spend 10 hours a day in the film room? He'll do just enough, but he needs to do more in order to overcome his height, and the fact that he's not built to take hits.
In the pros, he's going to slow down significantly once he starts getting dinged up. We saw it this year, he slowed down. Try that cowboy shit for preseason + 16 games... Without his legs, he becomes a short guy that can't move or see over the line... now toss in the fact he'll probably spend more time at parties than in the film room...