I don't think having a WR with more yards than an RB is inherently a problem, but definitely a shift from the previous philosophy. Surprisingly never happened with Callahan, although you can give him some of the credit for it happening in '08 as well. Obviously more likely to happen with RB rotations, but in this case the run game just sucks as well.
In 2015 the top 4 rushers had 765, 444, 400, and 265 yards. In 2008 they had 803, 517, 467, and 258 yards. So 1,800-2,000 between the top 4 rushers, which I would be fine with. This year it's 431, 299, 259, 65. We do have 3 games left (and likely no bowl game, where the other years did have to boost the stats), but we're not running for 800 yards in the next 3 games anyway. It's not the rotation, it's just a pathetic running game.