Not really. Marcel had good games, but gets worn down. It's not like many other players (Adrian Wilson, the entire O-line, the entire D-line, etc.) who had miserable seasons as a whole. Marcel has shown that (1) he can't stay healthy, (2) he fumbles way too often, especially in the red zone, and (3) he can't break open the long run. I'm still suspicious about his ability to score when someone that's not Thomas Jones sets up the two-yard dive for him. The lack of TDs can somewhat be blamed on Sully (but not busting a 20+ yd TD run in 230 carries is pretty questionable in a so-called "Franchise" running back), but his overall lack of success can only be blamed on lack of talent.
I'm still not sure that a one-back set won't expose his lack of speed even more so. Hard to get those holes in the middle if you don't have a FB making them for you.