I think Barber could do everything a feature back needs to do if he's given the opportunity, I mean let's not forget this is his 3rd SEASON! It's ridiculous that anyone could classify him one way or the other when he hasn't had a chance to.
People have compared him to Troy Hambrick, which is just plain stupid since no one knew Troy Hambrick would suck as a feature back until he actually got on the field in that role.
The NFL is full of people in a starting role that at one time were considered inadequet for that roll (See Marques Colston, Rod Smith, Marc Bulger, etc) and plenty of highly drafted players that were not cut out for the feature role (See Charles Rogers, Robert Gallery, Ryan Leaf, etc)
You simply can't say he would be bad or good until you see it, but you can certainly see the potential there to do well.