Let's not kid ourselves about Mitchell and pretend he's overrated.
The guy played his ass off in the playoffs, and played his best basketball when his team had their backs to the wall. Dropped 22 in the 3rd quarter alone in Game 5 against the Rockets before leaving with an injury. He's a big game player and will only get better.
Anyways, agreed with the OP...Mitchell and Tatum are both better than Simmons.