Koru-moru and Joachim are not primary healers; Koru-Moru's main role is to buff and debuff, with the occasional dabbling into cures. Joachim's is to sing first, then heal (though admittedly, when he's doing nothing but chucking our Traverser Stones, he still is a bit slow on the heals). Kupipi is one I'd have a genuine concern over, but I've had no issues with her healing up until this point; generally, she's a little overzealous with healing if anything, often casting -na spells before I've registered that they're there. I'm not sure what her issue is with you, tbh.

But yeah, the latter two should not be looked to for main healing. Their AI is not built to main heal. Main healers are Trusts like Ferreous Coffin, Cherukiki, Mihli Aliapoh, etc. I'd say Kupipi too but you seem to be having an issue there.