I see no reason to worry about D-Mac (other than injury). I've never seen an offensive scheme revolve around 1 player so completely. He will get the runs. If he can't run, he will get the passes. If he can't run OR catch, they will let him throw it. If he can't run, catch OR pass, expect to see him on punt returns or in the secondary hawking interceptions.
If any team (other than Jacksonville) featured a RB the way Oakland features McFadden they would have the #1 RB in the league.
Sadly, he's still just a #2.