...Perk are a key strength of that team.
less than 5 points and less than 6 rebounds in less than 27 minutes for over $7M (and going up) is a strength of the team?
I don't see how you can conclude that Perk is a strength of the team (leaving Ibaka out of it for now who is only slightly better statistically). By strength, does that mean a primary reason they are winning? The guy the other team game plans around? Making his teammates better? Instilling toughness?
He's one of the better defensive bigs in the league. That might not count for much to some, but it makes a difference in the standings.
Perk IS a key strength to the Thunder, but he would be a liability on the Celtics.
It's all about how a player fits into a team, how his strengths and weaknesses complement / are complemented by the team's strengths and weaknesses.
Having a front court like the Thunder do works because they have such prolific outside scorers. They don't need scoring bigs because they have a point guard who is probably the second best scorer at his position, and a small forward who is the best scorer at his position, plus a 6th man shooting guard who is extremely productive and efficient as well.
Since the Thunder get so much scoring from those spots, they just need a frontcourt that can rebound and protect the paint, while finishing inside at a high percentage when they do get a clear look.
On the Celtics, the lack of inside scoring is a huge problem because they don't have one or two guys who stand out as truly elite scorers. Even in '08, when the Big 3 were younger and still elite, the Celtics were built to rely on balanced scoring across the board, though obviously skewed towards the Big 3. Now that the Big 3 can't be expected to each score 15-20 points a game, the lack of scoring at the other positions, particularly inside, is exposed as a weakness.