LeBron's ability as a defensive anchor really is quite overrated, and has deteriorated since going back to Cleveland (even in Miami, both Bosh and Battier had just as much importance, if not more on defense). Even in the playoffs, LeBron takes a bunch of possessions off and swoops in to crash the boards to prop up his stats and start the fast break. His man-to-man defense hasn't been shyt for a while now too.
The only real weakness in Durant's defense is he can be inconsistent. Otherwise, he's been the better defender since probably 2015.
Yeah, he definitely phones it in and takes possessions but he has ungodly high basketball IQ, experience, and the ability to turn it up when needed. Lebron's vision, decision making, athleticism, size, and versatility allows him to blow up plays in the most unexpected moments. Lebron is also great at using the threat of his presence to deter shots and make players second guess their decision.
I don't find him overrated. He's definitely a defensive fulcrum and hos versatility is the lifeblood of their defense.
Bosh was ungodly amazing as a rim protector but we saw Lebron step in and still anchor the defense when Bosh went down against the Pacers. His rebounding (Especially in the playoffs) and ability to play bigger than his size was key to that defense because it allowed Bosh to stay mobile.