I've been thinking a lot on which healer being Luka or Refia for main team. Luka has a better tm in my opinion. Then considering we have the tms to do this: luka equipped with a ribbon and dual cast materia would be slightly better than refia equipped with the same (the ribbon would essentially be wasted on Refia). The HP difference from Refia passive and Luka not having a passive is quite marginal honestly being around 200 HP in which wouldnt save the healer if being focused. Luka has a pretty strong aoe ability for healer were as Refia does not. I personally like my healer to be able to damage in the case there isn't any healing needed to be done. As for buffs unless you're running strictly physical units then embolden might be better. However with new units being strongly magic geared lukas buff would be more beneficial. As well most physical units have a low SPR stat and boosting that would allow them to tank better against magic. I'm really kind of having a hard time trying to decide. I think baring tmr Refia might be better depending on situation and team. With tmr i think luka would be better for all situations. There are other factors that could play in but for the most part are really more niche than anything. When tilith gets 6* she will be my go to healer.