Only Rex can take credit for most of the best moves that took place, namely TT and Incognito. I like having Clay and Shady on the team, but considering the $ spent, I can't say that either acquisition has proven to be a slam-dunk success. Depending on your perspective, I would also give Rex the credit or the blame on Harvin. I will give Whaley the credit for Darby, though I have seen others say that Rex influenced the pick.
I'm not necessarily saying DW is a problem, I'm playing devil's advocate more than anything. I do believe his position with this organization may not exactly be rock solid.