People really underrate the effect a healthy Kevin Durant will have on their perimeter defense: he was a sub-elite defender a year ago. The guy gets injured one year and people seem to forget that, prior to last year's injury fest, the Thunder have consistently been a title contender with top five-ranked defense.
Durant, Roberson, a Westbrook who isn't carrying an insane offensive load and selling out on defense, theoretically Huestis, and even Waiters and Singler to a degree are sufficient for perimeter defense.