I'd like to add one thing to what you said.
You do bring up extremely valid points about what will happen to Durant upon DE's release. Durant will probably experience a very sharp decline in play due to what you just mentioned. However, someone I know brought up a very interesting point - the best time to play Durant is when everyone thinks it's dead.
So probably sometime after rotation, or whenever, when no one pays heed to Durant anymore as it's all but vanished, someone is going to perfect a Durant build and do amazingly with it. But yeah, it's still going to be in the minority.
Just an interesting thought. Now since this isn't a Durant topic, I'm going to step back for now from this discussion.