Not really his health, KD has always had issues breaking through double teams, he's a bit stagnant. He lacks the complete control over an offense that Steph and LBJ have. KD is a pure scorer, the other two run entire offenses. KD 1v1 all day every day, but there's more to the game than that.
KD left OKC for that reason, we got a glimpse of this last year again when he didn't have the spacing Curry and Klay provided him (make no mistake he still had talent offensively, Kyrie, Seth, Dragic Patty Mills, he has always historically had issues with doubles). Celtics absolutely embarassed him, they got destroyed by Steph, there is no defense for what he does, he forces defenses to step out too far to defend him, either he eats or there are free layup lines for the rest of the team.