It's pretty likely the Warriors would still only have just the one championship if not for Durant signing there. They probably would have lost to the Cavs again last year, and probably would have lost to the Rockets this year.
Durant might still have a lot to prove to a certain group of haters, but those of us being reasonable can see he's been the best player on that team the last two seasons, and the main reason they were able to win these last two titles.