Damp has always been a better rebounder. Blocking is pretty much a wash. Offensively, Rasho's range is countered by Damp's relative agressiveness.
The thing about Dampier is that he will always play down to the level of his compe ion, and when I say that I mean compe ion on his own team for the center spot. He was forever switching starts with Adonal Foyle in Golden State and he's doing the same with Diop in Dallas. He is clearly the better and more complete player in both situations, he just doesn't give as much of a as those two guys. So at some point, those guys displace him as starting C and fans, GMs and owners start overvaluing the out of those guys and start thinking of ways to get rid of Damp since he is underachieving. The result? $51 million for a scrub like Adonal Foyle. God knows what Diop is going to get two years from now....