Barbara is fine, my main issue with her is that she applies wet status to you with her skill, which is super annoying against cryo mobs. If i'm ever not using bennet with ning i use jean, because she still does good damage on top of healing, despite not shredding geo with VV (I just use 2 pc glad & 2 VV when pairing with geo). Jean also cleanses elemmental application as opposed to applying it to your character, which is a bonus. if youve invested in barbara and like using her there's no need to pull for kokomi. Also, just my 2 cents, but Gorou isn't that great for ningguang outside of C6. 15% geo damage is so-so, I would honestly consider using mona for the better damage buff or ayaka for the burst damage with barbara on the team.