I know the series ended a few days ago, and no one cares about it anymore other than the people who are going to raid the game footage for their Luke Walton highlight videos, but as a follow up to my (subjective) observation that Collison played much better defense on Bynum and Gasol than Kristic did, I took a look at each player's plus/minus numbers for the series.
Using traditional boxscore stats, Kristic looked better than Collison. Each player was on the court of 129 minutes, 21.5 a game. Kristic averaged 7 points, 6 rebounds, and a 14.6 PER. Nick Collison averaged 3 points, 5 rebounds, and had a 5.1 (that's not a typo) PER. And yet (per ESPN's boxscores) plus/minus tells a completely different story, with Kristic at -41 for the series and Collison at +33.
Small sample size caveats apply, but I think it's safe to say something was going on here, and there's a good chance that something was what I noticed subjectively-that Collison was not allowing whichever Laker big he was guarding to get good positioning down low, while the Lakers were dominating down low when Kristic was in the game.
It seems that Scottie Brooks might have noticed this too, because after subbing Collison in for Kristic in the third quarter of Game 6, he kept Collison in for the rest of the game. Initially, it seemed not to matter because, even though the Lakers couldn't get anything going inside, their scrubs got hot from downtown (the Lakers went 12-24 from three on the game). However, Collison's defense, and a couple of absolutely beautiful picks he set to free Durant and Westbrook for key three pointers down the stretch, were a big part of what allowed the Thunder to catch the Lakers and almost win the game. All of which just goes to show that a player with a 5.1 PER can be valuable.