I think the question celtics (and others) are making themselves is: can a westbrook-lead team win it all?
If you take a look at the games were Durant was out with injury, the answer is an easy no: too much hero ball.
Just like Iverson, Westbrook will most probably go down as a fan favorite without a ring. Just like Iverson, he needs the ball in his hands A LOT, and while that makes subpar teams stay afloat, it prevents them from growing, as well.
So there you have the reason OKC is looking at pennies on the dollar offers...