Agree Mickey deserves a shot as an inside guy. Though the knock on him has been his D. I don't know if he's the answer, as he's undersized for a center.
Horford is a fine player, but he's no big rebounder. Never was in Atlanta. They need a big guy to get the ball, as they don't have good enough outside shooters to make enough first shots.
The situation is kind of like when the Celtics had Ed McCauley in the middle. They had a ton of offense, but McCauley was more O than D, like the rest of the team. So Red traded for Russell, and the rest is history. They became unbeatable with the big D guy in the middle.