I think there is too much of a rush to judgement over Kanter's defense. Yes, it has been bad his first couple of years in the league but he is still so young.
I think there needs to be more patience with Enes Kanter's defense. He is still a very young player. He has been on some dodgy teams (defense-wise). Played under unconvincing coaches. Over the last year he was being switched between PF and C which are very different positions in terms of defensive matchups and duties. His minutes have been all over the place because he was competing with Favors. An unsettled situation.
The last 3 months of the season was his first real spell at a strong defensive team playing his natural position (center) with starter's minutes. It's the next year or two that are really going to define his development and what he can be in this league. Not the past few years. Kanter is a guy with potential and you have to pay for that.
I think he has the capacity to be a solid defender. Kanter has good strength, decent size and good quickness and mobility for his position. Kanter will never be a great shot-blocker but there is no good reason why he cannot become an otherwise solid defensive center. Next to Ibaka (a top defensive shot-blocking PF), that is all OKC needs defensively from Kanter ... especially given what he is capable of offering as an offensive threat.