It would depend on which healer classes you have in your raid of ten.
I remember reading, back in WotLK... when we had several 10-boxers doing current 10-man content... that the healing was the challenge.

If you have AoE classes, with Chain Heal or Wild Growth that automatically arc to whoever is most hurt...
That is a good idea to use on cooldown, possibly assisting the tank and casting at Target's Target so the tank is the initial hit.

You could create the equivalent of Slot X target me mapped keys.
Basically copy your FTL Target Me mapped key, but change the target so its only one slot instead of all the others.
I've done this for Slot 1-5 Target Me and Slot 1-5 Assist Me.
You could create a multistep mapped key, where Toon A does Slot X target me, then Toon B does Slot X target me...
Which would allow you to put Rejuvenation, or something similar on the entire raid.

If you have a Disc Priest, you could go with Smite spam... which while not optimal DPS, also heals the most hurt toon.
That could balance out, maybe.