As much as RR said he could "adapt" his offense to a pocket passer (e.g. Threet), it is pretty obvious that it runs much better with a dual-threat at the controls regardless of stated rhetoric. The great litmus test for this concept is Florida who runs a similar offense which has been established for a number of years, has a fourth year Jr, pro-style QB at the controls, and is stock full of multiple highly ranked recruiting classes. Considering that Florida, with all the above advantages, is also struggling with this transition. It is pretty obvious this system only fits a guy that can also run which is not a bad thing, simply the way it is. This message is gaining more mention over the "internets" regarding Urban's offense with Florida's beat down at Alabama coupled with their struggles this season.
When I think about Florida struggling under optimal conditions, I can only believe there was really no hope for RR year one. I am surprised we even had any offensive numbers after installing a new system with a thin oline and inexperience at QB along with the wrong type of athlete at the controls. It honestly could not have been a much worse starting point.
Edit: Thought Brantley was a Sr and is only a RS Jr. The guy is still in his fourth year with the system.