Feel like the Simmons fit in Brooklyn is not as much as a slam dunk as everyone is saying. That's adding another non-shooter and a free throw risk to the lineup alongside Drummond, hurting their spacing, and Simmons simply can't really play off the ball.
I think you'll see Ben most effective with only one of Irving/Durant in the game, with a questionable fit when all three are playing, especially with another non-shooting 5. You almost need to play Simmons at the 5.