Why would we give up AB for Butler? I would like to hang onto AB since he's our best 2 way player.
Butler is a better 2-way player, period.
Technically, Bradley is a better defender and might be a better shooter.
It was interesting hearing Sean Grande talk about Butler. He said Butler isn't as big an upgrade over Jae Crowder as people think. Consider some people think we'll need to give up#3, Crowder AND Bradley to get Butler. That could be a pretty big set back.
If you're operating under the premise we need Butler to get Durant, I'd argue that we should just explain to Durant how his impact would heighten the efficiency of players like Bradley, Crowder and #3. No need to take a big step backwards to take a big step forwards.