Yeah, I was aware of the buff cross over issue with a few of those. Tesla in particular could still be run in an alternating fashion with elimo though. Lancia's attack buff has been fairly redundant with the advent of Vargas's 6* form, never mind michele's being superior in general. The crit buff thing, well, that is its own animal and I'm not entirely certain the crit teams even run a healer given the focus of them. I mean, you got what, michelle, GX, the centaur, potentailly douglass, Loch, and a few others already competing for the remaining 4 slots available. I'm not entirely certain there is room for a healer there and simply frontloading more damage seems more productive/synergistic anyhow.
Between tillith/elimo and melchio, I could see not needing a tree, but that could be a specific build too. The important part for those healers is the fact that they do massively burst heal in addition to other useful effects and aren't terribly squishy. I mean, not everyone can be like lunaris, golem, kaja, maxwell, etc...