Alright, I beat Solomon/Goetia. It took me quite a few attempts to get a winning run, a lot of it seems like it just came down to luck on which attacks he uses, since he kept using his strong AOE attack three times a turn for multiple turns in a row and I just couldn't keep up with the pressure, but I finally had a run where he mixed in a lot more of his multi-hit AOE attack and that let me charge Jeanne's NP enough to stay afloat. I used one command seal for safety on a turn when he might have been able to NP me if he used his charge skill and it's a good thing I did because I definitely would have died otherwise because he totally did do that... Aside from Jeanne my MVP was Ibaraki, she just would not die and must have taken down like 2/3 of his health bar by herself...
On an unrelated note, did anybody watch the first episode of the Babylonia anime? It's on my list but I think I lost track of which streaming service actually has it.
Edit: Oops, I guess Goetia had one more final form. But after the previous one it was no problem.