the problem for the thunder is that presti made desperate moves and only cared to get westbrook to sign to save himself. He lost Durant and harden for barely anything and westbrook leaving would have killed his career as GM. So he did what any desperate GM would do and make trades that are detrimental for the future but looks good on the current year.
By trading for a year rental, Presti showed westbrook that he wants to win, and westbrook dumb enough fell for it. PG is gone, Melo is a black hole with a horrible contract and will opt in unless he really wants to win a ring.
OKC has no prospects, late draft pick and no cap space. They are going to lose Grant cause they won't be able to afford him even if pg stays or not. The bench is laughingly bad. They have no star to come off the bench. They have paterson, felton, abrines, huestis as their bench guys. So pretty much a bunch of nobodies coming off the bench.
And to top it all off, they are sticking with Donovan cause they have no other choice. They don't want to pay two coaches and are willing to ride him till his contract ends.