Why do so many healers not use specific abilities?

[tdb]

I could be misunderstanding and if I am I apologize - you mention if Medica II is ending or has just ended you will use it but if not you use Assize/Medica. While I would never fault anyone for overhealing via Assize if you have a Medica II ticking you don't then cast Medica, do you? It's not super clear, as I said I could just be misunderstanding.

Did you perhaps read it as "(Medica II or Assize) then Medica" or "Medica II or (Assize then Medica)"? The intent was "Medica II or Assize or Medica" - i.e. it was a description of how I choose one AoE healing spell to cast when the party has taken significant damage. If that wasn't enough to bring the party to satisfactory health levels I'll cast another, but I won't waste MP casting Medica if it isn't needed. It's hard to quantify how much damage is significant enough to warrant an AoE heal; it depends on the flow of the fight and how good the others are in avoiding AoEs. My experience is undoubtedly colored by playing with randoms since my FC doesn't have enough active endgame players to form our own raiding group yet (but several members are my IRL friends so I'm sticking with them).