Why do you think that Bush won't be a very good NFL back? He isn't small and he hasn't been shown to be fragile. Big backs get hurt a lot too.
Bush isn't "small" at all. In fact, that's part of his problem . . . I think he "runs too tall," as they like to say in the NFL. He doesn't have that wide, squat frame and low running style that you see in all great NFL running backs. If I were an NFL general manager, I'd have White higher on my draft board than Bush.