Daniel Thomas has been running hard, and I've always rooted for him and thought he was being shafted by poor blocking and his situational use limiting his YPC. There's never been any reason to cut him, but I do think that when it comes down to it, those who say he is a replacement level back are right. He can gain the yards that are there to get, but any NFL caliber back would be able to contribute roughly the same.
I don't think you could have made a case for cutting him when he understands the offense, does a lot of little things that don't show up on the stat sheet well, and as I said before he gets the yards that are there. But watching other teams go 3-4 down their depth chart and realizing that those guys have the same ability as Thomas makes me understand those who think that other backs would be more productive in his place (I don't think our line has the ability to make many backs truly exceptional, at least on average).