The only argument is that having to beat LeBron and then ONE of the Western Conference contenders is an easier road to a title than having to beat 2 or 3 Western Conference contenders and THEN beat LeBron on top of that.
No team in the East can offer Durant the level of talent his current team already. But playing in a conference with only one other team that has any hope of beating you in a series means your odds of winning a title are much higher.
Aside from that, the only point I can see on this is that Westbrook might bail next summer to have his own show somewhere else (LA or NY probably). Maybe Durant knows that's likely to happen, and so he decides to leave this summer so he can start building experience and chemistry with a different team, probably in the East.
I still feel like Westbrook is a bit overrated... and he's the main reason people say Durant can't find a better supporting cast. Honestly, I'm not sure Westbrook's talents compliment Durant as well as some people think. They never really seemed like a great fit together.
Someone mentioned in another thread, the Thunder without Durant would compare well with the Blazers. The idea is that Westbrook is similar to Damian Lillard. Lillard is a more efficient scorer, though... and the Thunder don't have a CJ McCollum lighting it up at the SG position. Actually, the Blazers might be one of several teams that would provide a better supporting cast than Durant has right now in Oklahoma City.
Westbrook and Durant aren't an ideal fit. They both have a #1 game and all they've ever done is take turns.
The thing is, it really doesn't matter. Having two top 5 talents on your roster is better than having a top 5 talent and some top 20-30 guy who complements his game.
Not to mention, Ibaka / Kanter / Adams is a pretty great, young frontcourt as well, plus they have Roberson and Payne on the come-up. OKC is in a pretty good position moving forward as long as they can figure out how to manage their cap sheet with all of these guys needing to get paid.
And by the way, I love Damian Lillard, but he's nowhere near the player Westbrook is. Westbrook is 80% of an all-time great, and the other 20% is unbridled chaos that is pretty much a coin flip as to which team it helps and which team it hurts.
Lillard is a great leader on and off the court, and he's a wonderful scorer. He's not a good defender and he doesn't have the raw talent and athleticism to put up numbers regardless of what the other team tries to do about it. Westbrook does.