Decided to take one more swing at it after seeing lots of people saying that playing on Merciliess is the answer.
It's definitely part of the answer: I got past the green guys.
But then I got one-shotted by the next wave.
At that point, it really seems to come down to RNG. If you have time to prepare for the big attack, you are golden. But if you were just randomly debuffed three times and have to deal with that and prepare for the big attack, you will die.
Playing the same fight over and over again hoping to get a better RNG is not fun and I will stand by that. Atlus decided to add a not-fun gate to their game where you have to beat your head against a wall for a while until they randomly let you through back into the fun.
So it's really Atlus's fault that I'm quitting and not mine at all.
I watched a video essay thing about how broken and terrible this fight is and, while I lack the SMT street-cred this YouTuber brings to the table, I completely agree. It's badly designed and should've been fixed in a patch or something.
Anyway, life is short. I'm moving on. For real this time.