That was the one often overlooked advantage of Harden in his OKC form, he basically wrecked up their passive style with his aggressive style and they didn't have to rely on just the efficiency of Durant (and to be fair, Westbook many times) for their offensive attack. He also allowed Westbrook to move off ball and still get his shots only he wouldn't pound the ball into the floor.
To be fair, the Spurs were sorta this way before Manu really kicked in, and then they built deliberately around being able to play multiple styles which requires you to be able to move the ball.
With the Thunder you don't have that confidence that when Durant has a poor game, someone else other than him, Westbrook and Ibaka, is magically going to get the 15 points they need. This almost always somehow happens for the Spurs. Even Miami was getting that from Ray Allen, etc. at times.