It’s not just about power, it’s fatigue as well. The bigger the rotor, the less force you have to apply to the levers to get the same power, yeah?
If you’re doing a lot of runs in a day, that will help to keep you relaxed. So many people on here go to great lengths to increase comfort and decrease hand and forearm pain (hundreds of pounds on carbon bars, ESI grips etc etc) – yet simply going up a rotor size would do a lot for them over the course of a days ride or dozens of shuttle assisted runs down a rocky downhill track.