Gojou should know all of this. He has seen a number of times Marin transform into another character when cosplaying. She's not just donning the clothes, she assumes the role. That's why people respected her cosplay so much, in addition to appreciating her natural beauty and the high quality costumes, of course. Even the infamously difficult to deal with author of the fallen angel novels actually approved of her cosplay. Gojou has witnessed all of this firsthand, including Marin repeatedly switching on and off if Juju happened to be present, since Marin never managed to maintain her cool long before turning into a fangirl.