Wouldn't put Dirk or Amare up there. Neither of them plays D. Either one of them is just as capable of giving up 30 as he is of pouring in 30.
Joe Johnson, maybe - especially the way he's playing this year.
Tracy McGrady when he's healthy, personal dislike aside.
Those would be my replacements on that list, I think.
Anyway, to the actual topic: The problem I have with Pierce is that he can be shut down. Kobe really can't. Same with Bron, Wade, CP3, healthy TMac. For that reason, I'd stick him sixth behind them, keeping in mind that this is based only on ability - if I could sign any of them to a one-year contract, I'd take Pierce above Wade and McGrady for health reasons.