he doesn't actually.
cornermen are only useless if they're bad, you don't listen to them, or you don't have an understanding of each other. Perry has had a bit of all these going on in his career.
Perry has clearly just never had a quality coach that he connected with. He's called coaches useless and shit but thats just incredibly dumb. He's talking about how he likes quiet and calm in this video. Find a fucking coach who can do that and tell him to talk with you like that. Maybe he's the problem, not every coach he's had? This dude has a lot of raw fighting potential. He could be so much better than he's looked in many fights.
A corner is far from the most important thing but not having one is purely a liability and you can't afford liablities at this level. Mike Perry just got touched up by Mickey fucking Gall for ~8 minutes. Didn't have anything to do with no cornerman but surely it had a lot to do with not having a real coach or camp. he looked so stiff and his range finding was terrible until round 3 when Gall did his usual gassing. Looked like he had no proper sparring.
Honestly that's got to be one of the career worst performances for Perry after he just had career best performances against Brazillian Cowboy and Luque not too long ago.