I don't buy it completely. There is a real chance that Duncan hangs it up after this year, and if so San Antonio will be a worse team.
Harrison Barnes might also leave GSW, and while that isn't a huge loss, it does weaken them.
Durant and Westbrook on OKC are a top 4 team in the NBA. If the two scenarios above happen, they could be top 2. Where does Durant go, besides GSW, to put him in a better situation than that? There isn't another team that offers more than his current squad because they have Westbrook.
The only reason I do buy it is if Durant believes that he can't get there with Westbrook (or with Billy Donovan as coach -- more likely). If either are true than it makes sense to leave, but again I really don't but that he will have a better chance anywhere else than OKC.
There's also the possibility that Westbrook leaves the following year. Does he think Westbrook shows as much loyalty to OKC as he might? KD could sign a long-term deal only to be stuck in OKC without Westbrook after next year. Or ownership might decide that they're done with the luxury tax, and not make any other improvements.
I do think KD should go East if not to Golden State (and not just because the most logical team is Boston). The Spurs aren't going anywhere (they're 14-2 without Duncan this year, so while his retirement would be a loss, it wouldn't be disastrous). Golden State obviously isn't going anywhere. The best path to compete for a championship is going through the Eastern Conference, be it Boston, Washington, or some other team that figures out how to create space for him (Toronto?).
We need an actual separate thread/poll for this question. I'll try and make one tomorrow.
Depending upon how you feel about Golden State's fit (theoretically, it's a good fit - but how can you account for personalities and whether or not Durant, Curry, and Thompson, let alone Green, will not have problems with fewer overall touches?), I think it's a pretty solid argument that Boston is the best place for him in the East.
Our two main competitors would be Washington and Toronto. Even though he's from there, I don't think Washington is a legit destination for him anymore, because they've looked terrible this year. We're clearly a better team than them, and they also have question marks with Wittman as a reliable coach, Beal's health, an aging and less-than-stellar frontcourt, and the ball-dominance of Wall and Beal.
Toronto is a little trickier, because a starting lineup of Lowry, Derozan, Carroll, Durant, and JV looks pretty tempting. However, Lowry and Derozan are both high-usage, ball-dominant players, and I don't know how well that will translate to Durant. Also, Derozan is a question mark this summer, though it looks like he'll be back. It's also Canada and freezing, so we'd even win the weather/destination route with Toronto.
As for us, he would seemingly fit in perfectly with us as a small forward or small-ball 4, and we really only have one player that is high-usage and ball-dominant in IT, though he can successfully play off of the ball, too. Further, we also have room to add another max-level guy next to him, and coincidentally he's made it known that Horford would be one of the players that he would like to play with. A lineup of IT, Bradley, Crowder, Durant, and Horford with a bench of Smart, Turner (resigned), JJ, KO, Mickey, and whoever we get from the Brooklyn pick (if not traded for another star) is going to be scary good and balanced, and I think we'd easily be the favorites in the Eastern Conference over the Cavaliers.