The problem is that you're expecting the healers to be in-combat healers - and they're just not. Sometimes you can get away with it, but most of the time you're inviting them to ring the big *DING*.
If you're going to use hires, then you have to either learn to always park them somewhere safe and use them for after-combat* healing, or be willing/able to raise them yourself. Just that simple.
(* If you park them on Active, FAR away from any tempting targets or respawns, then you
might be able to summon them if a battle is going badly, and they
might wake up and heal your dying butt. But it's
much better to become a better player and learn to run away if a fight is going badly - fall back, find a safe spot, call the hire, heal, and dive back in.
Or have a high enough UMD to use RD scrolls on your hire - that works too.
)