Hey folks. I've had this exact issue for a while, and this seemed to help make it much more responsive for me:
- Navigate to your Logic Pro X app in Finder, Applications folder most likely. Right click on it and click Show info. Tick the "Open in Low Resolution" checkbox.
- Next time you open Logic it will look a bit worse but performance should increase slightly.
I tried this step to fix an unrelated problem, I was getting audible pops and clicks during recording that wouldn't be present during input monitoring. And it seemed to help both cases. Hope it works for you as well.