Using Ea over Sol would already be a big damage increase. Ea may be a pretty meh SSR but she is still an SSR. Using Ea, or Bephegor, instead of Sol, can be the difference between pushing a boss out of rage before it overdrives you or not, not only because of them doing more damage but because they can reduce the rage meter by a large amount with a single skill. Using Sol who is not only a weak attacker but as an off element hime will reduce your damage output in which reducing the rate you can push out of a rage phase. Sure you can use Sol to heal the overdrive damage, assuming it doesn't insta kill you, but how about just bypassing that damage altogether while still doing more damage?

As for what soul you should go, it can change depending on who you plan to get if you're getting a miracle ticket but assuming you don't get anyone, Joan would have been my pick, with Black Prop as an ex skill. You have 2 sources of orb removals, BP, 2 damage cut skills and heals/regen. You shouldn't have any problems surviving fights even without Sol. In fact, you should have probably been using this team to begin with since you don't need Sniper Shot.

You can just try using Joan without her soul weapon to see whether or not she makes a difference for you.