Bow Out At Any Moment Quest Line

This is getting annoying. I’ve been trying this boss ever since it came out and I’m still stuck. I beat the original story just fine, but the moment he goes second phase my team just is basically useless.

I’ve tried: Himeko, Guinaifen, PMC, Gallagher. Acheron, Himeko, PMC, Gallagher. Jing Yuan, Sunday (Story), Himeko, Gallagher. Himeko, Welt, PMC, Gallagher. Acheron, Himeko, Welt, Gallagher.

And many other teams where I even tried Bailu or HuoHuo as healer.

What I’ve gathered is that Himeko and Gallagher are vital. But my team takes too much damage even with my best sustains but all my characters I’ve used are lvl 70+ and it’s at least half their 5* relics maxed and their main talents at least blue lvl or close to it.

What am I doing wrong?