I'm sure Sam Presti is kicking himself for extending Perkins contract. I love the big guy, but he has been a shell of himself since we got him from the Celtics. We really needed a low-post scorer this series. Randolph and Gasol are just too good. I think we could of won the series had everyone showed up on the same night, but the inconsistency of shots falling and rebounding was a like a checkerboard amongst our roster. As for Durant, he was just tired. He was 5 of 22 last night. Kevin Durant, the second best player in the league, was 5 of 22. He short-armed a lot of shots and got throttled by Memphis' defense. All the credit in the world goes to Memphis for that.
The fact that Tony Allen, an All-NBA defender, was on him a lot certainly didn't help matters. Memphis game planned for Durant and did one hell of a job, I totally agree with you there. But yeah, Perkins was vastly overmatched this series. A few years ago, having Perkins on the team made sense -- he was the veteran anchor, and a pretty good defender -- since then, the guy has taken a significant step back and probably shouldn't be more than a back-up center. Their other options aren't much better -- Thabeet isn't exactly very good either, Randolph and Gasol were far too much for him to handle on the block -- and aside from maybe a small-ball line-up with Ibaka at the 5 and Collison at the 4, OKC had no viable line-up options to play against the Memphis bigs. Gasol and Randolph were too much for the Thunder.
EDIT: Tayshaun Prince did a surprisingly good job defending Durant, too. I'm too lazy to find the stats, but Durant had a tough time against him.