Proposition: the Clippers cannot
There is a good chance we can pass Miami and OKC in 3 years sure.....but this is a stars league as I know you're aware and we aren't going to have a Curry/Klay/Dray or a Blake/Paul/DeAndre or a Kawhi/Aldridge combos anytime soon. Over time those players are either remaining with their team or in the case of LAC possibly moved for returning talent if they ever break up the gang.
If Durant wants to rebuild a roster yeah sure I guess that's a nice challenge for him......being in place with any of the other teams he's meeting with make him an instant championship tomorrow AND throughout the length of his contract.
The Celtics were equally as good as Miami last year. They have a younger roster and the space to add an additional max player in addition to Durant as well as a dramatic draft pick advantage. Sure, Miami did better in the playoffs, but the Celtics suffered serious injuries in the playoffs that derailed their chances. It's hard to imagine a reasonable argument that Miami is a better potential destination. It's actually hard to imagine why Durant is even considering Miami.
In general, it seems like you are dramatically underweighting the Celtics' ability to add a second max contract player, i.e., Horford. The current Celtics team, plus Horford, is definitely better than Miami. They are probably competitive with the Clippers. They are not as good as the Warriors and Spurs. It's a closer call how they compare to a Durant-less Thunder team, but they may very well be better than them too. If we assume that the only two teams who are actually better than the Celtics in this scenario are the Spurs and Warriors, it gets more interesting. The Spurs are a terrible roster fit. Kawhi, Durant, and Aldridge are all forwards, which means that both Durant and Aldridge would probably need to play up a position defensively to make the roster work. That both locks them into being undersized and asks Durant to shift permanently to the 4. (Kawhi is probably the guy who should remain at the 3 defensively.) While Pop is a great coach who can probably work around this, it's a legitimate point of concern that Durant might have. Additionally, the Spurs roster is aging out and they won't be able to continue to steal value from their old core who have decided to play at discounts as they sail into the sunset for much longer. The Warriors roster, with Durant, is formidable. If all he cares about is winning, that's absolutely where he should go. The only real argument against them is grounded in ego/legacy and I don't think I really need to run through it.
In the end, I think it's pretty likely he stays in OKC for at least another year. They were close this year, have already improved via the Ibaka trade, and can pay him more. If he leaves, I would be shocked if it is to go anywhere besides to the Warriors or the Celtics.