When you talk about Elite talent, it means they have something not many other players at their position have, consistently every week.
How many players can get their ### 12 inches off the ground like this, 
http://screencast.com/t/SpSjNOkFlJ. Maybe you can count on a single hand? Imagine being a 6'6" DE trying to tackle that in open space. Forget it. Even a 6'2" LB guy is going to miss 9 times out of 10. Shifty smallish corners even have trouble tackling him because of his adequate power combined with this shiftiness and balance. Nobody has a lower center of gravity which is a key elite advantage he has over most if not all RBs. then couple that elite low center of gravity balance with adequate power and great pass catching ability with shiftiness to be compared with some of the elite RB greats of our time. He is not in the mold of Gurley or AP, he is in the mold of some great backs of the past, however in running style, and many of those guys did not have the pass catching ability he has so the potential is tremendous.
MOP mentions that he is a product of the system, but if this guy was on KC instead of Charc he would be doing even more IMO. HE would have 20+ carry 25 touch days that would be astounding on a poor team that focuses on dump offs to the RB. So yeaah I think he is somewhat limited in upside because of being in NE because of lack of touches. That goes against your entire argument I know, but its true. Put him on any team that gives him 20-25 touches a game and he produces. Heck even 15 touches he will produce. He makes 2-5 guys miss on a single play routinely so that is not system, that is all him. ELITE TALENT!
EDIT to add, I know he gets points from being in NE system which is ultra efficient so this mitigates his lack of touches somewhat, but if he got traded to the Cowboys tomorrow and supplanted McFadden he would out-produce him easily. We do have to credit BB giving him his shot though. I think after 2-3 years of this even if he is traded he will be a major part of any offense that picks him up so I am not convinced he will lose all his value if traded to another team, even though we must credit BB for shining the light on him. He passed through 3 other teams that cut the guy, but he was always talented. Just needed an opp.