One method of tiers I like is "can you picture winning the title with this guy as your {x}"?
Tier One is "best player" and that easily includes Jordan, LeBron, Duncan, Shaq, Bird, etc. if only because they all did it, multiple times. But theoretically this list can be large and/or season dependent, ala Anthony Davis a year ago vs. this season. It's also where you see a guy like LeBron a year ago, with his team in shambles against an unstoppable juggernaut and somehow still making them work to knock him out. Not to mention getting to the Finals in the first place.
Tier Two is "second best or equal player" and that has a bit more nuance to it. Like Karl Malone, for example, I can picture him as being in Tier One. But I can also see the case that he's not enough to get you multiple titles (went to two Finals, couple Western Finals, might have grabbed one against someone other than Jordan, Hakeem, etc.) but if you had two Karl Malone's that changes things. Obviously having two Malone's is hard to work literally, but if you take it as two players of that level type of thing. (And the Jazz in many ways did with him and Stockton, but if neither are in that first tier and they run into a team who has that player...and one of their guys underplays...)
The 2000-2002 Lakers obviously had both a Tier One and Tier Two guy, so even as the rest of the team atrophied they could still smack around teams who couldn't throw anything higher than a Tier Two (Webber or Kidd for example) at them.
Tier Three would lead to something like the 2004 Pistons or Bad Boy Pistons or 2008 Celtics, where they had really good players, but nobody who was parsecs above anyone else and could lead a team on their own, but combined their top three, four, even five guys were all top tier enough (and the teams deep enough) to where they could survive with just one of the guys stepping up a Tier or two every game. So they had so many guys who could be the "third or fourth best player" on a title team that they wound up being able to crush teams with higher Tier guys but fewer total Top Three Tier guys. The Heat, Cavs, Warriors, etc. are doing forms of this but with higher Tier guys at the peak. The Spurs have sorta done this over the last decade compared to their earlier MVP Duncan era. Often times these teams can have guys who move up into this Tier or higher for just a couple seasons and then some other player replaces them. The 2008-12 Celtics were kinda like this with Rondo eventually moving up and KG and Allen slipping.
I think Durant still has all the potential of a Tier One guy. But he might be lower on that totem pole. One of the Tier Ones who needs a legit Tier Two or two backing him up. He had that probably with Westbrook, but never had the third guy to lock it in (Harden was too early, Ibaka flat-lined, etc.). And they ran into lots of good teams as well.
I look at a team like the Clippers and I think, they've got a probably Tier One guy in Chris Paul, Blake Griffin is Tier Two at best, and DeAndre Jordan is Tier Three. And every year they run decent on the rest of the roster for the most part. But they always run into some problem and get derailed. But they've been in the mix ever since they got Paul.
But back to Durant, he can transition like LeBron did when he went to Miami, be more of a playmaker/in the flow/more efficient-less prolific type of things. And then when he needs to go into beast mode because others are floundering, he does so. LeBron's heralded playoff moments came from him playing alongside other All-Stars/All-NBAers/superstars and still dominating the game at an epic level. Nobody points to his Cavaliers eruptions when he was doing it alone and putting up ungodly numbers as being superior and it doesn't have to be different for Durant. I think the way he's taken over when injuries battered OKC and such makes it a good probability that he won't just start camping in the corner and letting Curry/Green run the offense. And the Warriors style doesn't seem like one that will fall into that "your turn, my turn, your turn, my turn, Chris's turn lol no your turn, my turn" that Miami first started off trying to operate with when LeBron got there.
One advantage is that we now live in the "positionless era" and Miami had to learn that instead of sticking to Joel Anthony and Mike Bibby because that's how you make lineups like they did that first year. Everybody does it now, Golden State doesn't need to bring back Don Nelson to play a Durant/Green/Iguodala front-line at times. Durant is much more of a rebounder and creator for his teammates than Barnes ever was. Barnes rebounded more like Stephen Curry than say Orlando-era Rashard Lewis despite both nominally playing the four. Bogut had the same number of assists in the playoffs as Barnes despite playing half the minutes. Ian Clark had half as many in one-fifth the minutes.
Obviously any titles Durant picks up in GSW will look tainted going forward, much like Payton or Zo's. But at the same time, LeBron's aren't as much as they were assumed to be heading in because of the stamp he's put on the last six Finals and how things have played out. Even though he played with max contract guys like Wade, Bosh, Irving, Love and Mozgov.
In other words, who knows? Certainly not any of this gibberish above.