Have you watched him play?
You are describing Newton at auburn to a T and saying it's why another guy won't be successful.
The only people who said Newton couldn't make NFL throws were people who didn't watch every game. Even Rivera said, during evaluation while watching EVERY throw from his time at Auburn, that Cam could make all of the throws.
RGIII is good. I don't know that he'll be as successful as Cam, but I think he'll at least be considered a solid starter, if only for impressive speed and arm strength. Of course, that is just me giving a broad, generic answer, as I've only seen two Baylor games with RGIII as the QB.