There's no denying Enes Kanter's productivity on offense. But, I'd contend that his problems on defense will most likely limit our ability to win a championship, no matter how productive he is on offense. Why?
DBPM is a rough defensive productivity metric. It's boxscore / +/- based. It's not perfect, but it's a rough estimate of defensive value. For our purposes it's sufficient here, especially since we've already established beyond reasonable doubt that Kanter is a very poor defensive player.

As you can see, Kanter's career DBPM is -1.9. We can use this to do an analysis on past champions. Here's a list of the past 20 NBA champions and the DBPM of their starting C:
Andrew Bogut: 5.5
Tim Duncan: 4.0
Udonis Haslem: 0.0
Udonis Haslem 0.7
Tyson Chandler: 1.7
Andrew Bynum: 1.3
Andrew Bynum: 1.6
Kendrick Perkins: 4.3
Francisco Elson: 3.4
Shaquille O'Neal: 1.2
Rasho Nesterovic: 4.1
Ben Wallace: 6.8
David Robinson: 3.3
Shaquille O'Neal: 1.5
Shaquille O'Neal: 1.6
Shaquille O'Neal: 3.5
David Robinson: 5.3
Luc Longley: 1.8
Luc Longley: 1.9
Luc Longley: 2.4
Zero NBA champions in this sample had a starting C with a negative DBPM, much less one as far into the negatives as Enes Kanter. But wait, you say. We can bring Enes Kanter off the bench. Well, here's a list of the worst rotation big men (by DBPM, mininum 1000 minutes played, minutes per game also included) on the same sample of NBA Champions:
Marresse Speights (-1.3, 15.9)
Aron Baynes (-.3, 9.3)
Udonis Haslem (0.0, 18.9)
Chris Bosh (0.3, 35.2)
Dirk Nowitzki (0.6, 34.3)
Andrew Bynum (1.3, 30.4)
Andrew Bynum (1.6, 28.9)
Glen Davis (1.1, 13.6)
Fabricio Oberto (2.2, 17.3)
Antoine Walker (-.6, 26.8)
Malik Rose (1.4, 17.2)
Corliss Williamson (-1.0, 19.9)
Malik Rose (1.2, 24.5)
Shaquille O'Neal (1.5, 36.1)
Horace Grant (0.5, 31.0)
A.C. Green (1.8, 23.5)
Will Perdue (2.5, 12.0) *** This Spurs team went thru a lot of bigs. Purdue is worst DBPM of the bunch with > 400 minutes
Jason Caffey (0.2, 13.9)
Jason Caffey (-.5, 18.7)
Bill Wennington (-.2, 15.0)
Here we see some negative performers, but again, nobody as negative as Kanter. Only six of the last twenty champions even had a major rotation player in the negatives on DBPM! Of those six, only Antoine Walker played more than 20 minutes per game.
It's clear, at least from this data, that re-signing Enes Kanter represents a big risk, and a faith that the Thunder can buck this twenty season long trend.
But wait, you say. Enes Kanter is only 23 years old, he will surely improve defensively. We can address this as well.
Since 1994-95 , 43 F and C have had -1.0 and worse DBPM through the first four years of their career (4000 minutes minimum):
http://bkref.com/tiny/ZHoLBThis isn't a fun list. Zach Randolph, by my estimation, is the ONLY big man on this list who would later mature into a capable defensive player. This didn't occur until he played for Memphis, his ninth year in the league.
Again, there are ways to massage this data. Maybe make it look not quite as bad for Kanter. But in my opinion, where there is smoke there is fire. Re-signing Kanter would be a very strong statement by the Thunder that they can either a) win a title IN SPITE of Kanter's current defensive ineptitude (a scenario unprecedented in the past 20 seasons), or b) improve Kanter's defense in short enough order to the point they can win a title (again, weak support in the data for this, at least in the foreseeable future).
Stranger things have happened, and Kanter is an exciting player on offense. The Thunder may be in a position where they have to keep him, just to appease Durant. But let's not disregard reason and precedent. Winning with Kanter would topple at least one, perhaps more, strong precedents.
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