Been playing around with AUmiYama a bit. They're never not going to be a 1/whatever/1 of course which is limiting, but man, that's a niiiice easy 400x after their active. Loaded up with prongs, decent utility... Not bad. Not bad at all. I finally have a nice brutal spike team to chew up ranking dungeons and some endgame content, and they should be monstrous in co-op. I honestly didn't expect getting a full activation out of them to be super easy, but with their active it kind of is.
Right now I'm using AUmiYama/Famiel/Orochi/AIsis/Alrescha/AUmiYama, with an ASusano active on Isis. Not sure if I want to swap one of the defensive actives out for something like Black Kali or AYomi, but it's seeming pretty solid so far. If the Famiel buff was out I feel like this would handle the current C10 quite nicely.
Edit:

These are genuinely not implausible numbers with an active. I was able to fairly easily hit this on turns one and two with just whatever was around.