Arcoris 2x is a harder miniboss, true, but I think a lot of that is how unique its behavior is. The rolling bullet balls are triggered by shooting one of their bullets, and their straight shots take a while to learn how to juke but are pretty easy to avoid (technically speaking).
When I get hit by them, I usually see exactly what I did to deserve it.
But misleading their aim can be a bit tricky and one of the bigger learning curves in the game, true. Still, I don't seem them needing a nerf. Might make for another decent reason to extend the range of our primary weapons slightly, though.