I can’t really judge Curry objectively since he’s never not been my guy, but with Durant I can draw on my impressions from his OKC days, and man, great as Harden is, KD always crushed him in the critical “scares the living shit out of me” and “please don’t let him face us in the playoffs” tests. The Warriors always had 3-4 guys who could hang defensively with Harden (Klay, Dre, Dray, Shaun, HBarnes); none of those guys could really handle KD.
And that’s just the offensive end. While KD has never rated as a great defender over a full season, in big games he has tools to make his impact felt defensively at a completely different level from Harden (or Curry). I mean, KD can and does guard Anthony Davis. Good luck with that, Harden and Curry.
Independent of context (which is what these lists strive to be) LeBron and KD have been the consensus two best players in the world for the last 5-6 years. Anyone who watches them even casually, on their teams or for Team USA, can see this pretty readily, and the efficiency/usage numbers pretty consistently bear it out. It takes a lot of overthinking, special pleading, and or click-baiting to put break up that pair, let alone drop KD to #4-5.
(TLDR: I agree with all of you).