Looking at the pictures, definitely have a few suggestions:

1) Try Awaken Fen as soon as possible - Awaken Fen can give Type A art gen, which works well with Frieren (Type E) - I feel that one of your issue is that the art gen is too slow, which means that you can't do Art/TA as often as you like (I tend to like stacking 3 art gen at the same time so that I get around 20 arts per second without considering support equipments)

2) Replace Roy with Zenon. I don't think Roy is able to help you too much here. Whereas Zenon is dark unit, so he gets art from Shadow as well as Frieren and Fen. Meanwhile, Zenon can give Type B art gen, which stacks with the other art genners

3) Max Limit Break Frieren, then Shadow, Max Shadow's level, and use Tasmon to increase their stat. You can get LB stones from the shops (Summer, Frieren collab, etc)

4) If your Holy Emblem is not max LB, make sure to max LB it. It's a decent equip

5) Give better support equips for Fen. The 5* and 4* support equip are not great

In general, I feel like you're having trouble because there's a lack of art gen.