Peterson's Oklahoma team did extremely well in his absence for a good reason. He's a nice physical specimen and a terrific athlete, but below average (yes, I said BELOW AVERAGE) in the most important aspects of being an all-world running back: patience and vision.
I don't know how many times Peterson refused to wait on a pulling guard to actually be in the vicinity of a block before he was stretching it further and further outside. Plays are designed with a pulling guard for a reason, and that's to allow a clear seam for a back to slide through. It completely destroys plays if a back wants to get impatient and try to freewheel.
The reason that Peterson's backups did so well in his absence is because they were more patient. It may have been from not being able to accelerate like Peterson, but what they were able to do showed that Peterson isn't a Barry Sanders, Gale Sayers, or even a Reggie Bush.