Again I keep wondering how fucked up any of this is. Unico took too much attention away from the hags? So what. It's a school festival, not a reality show where they're gonna get kicked off. The whole point of this event was to appease the student council. Mission accomplished, 100% success, ladies and gentlemen we got him.
Sumire made a limp boner joke? So what. They won't get invited back next year (good). The kids get something very memorable. And it's totally on brand with her youtube channel, where she gambles and fumbles through a medium she doesn't understand. This is a pratfall that should be promoted, because it's part of the appeal. "Hot woman cosplayer also does a clown act." It's entertaining!
Unico took too much attention, then Sumire brought it back with an awkward joke? That's cross-promotion. All the headlines of "Popular cosplayer shares stage with Rude Jokester" is clickbait$$$, baby. No such thing as bad press.
In conclusion, I think the "horror" is not the event itself, but the fallout. Ayumi and Souko and Sumire will find themselves getting a ton of attention and it will expose their questionable day jobs. Yuusei gets exposed for making ecchi books while in high school.