It's quite possible they are, but if your two available RBs are averaging 2.6 YPC and 4.6 YPC, why not at least give the latter guy a shot? Powell is, in fact, the only Cardinals back this year averaging over THREE yards a carry, let alone four. And they've given up 11 sacks in two weeks, so it's not like LSH is doing that great a job of keeping his QB upright. He's caught 2 more balls than Powell, so it's not a huge production difference there.
I'm fully aware that Powell is no superstar in waiting, and he may ending up falling flat, but it makes no sense to me that the Cardinals aren't at l