There's nothing wrong with running off to solo. I prefer soloing my monsters as black mage, actually. If I get low on health and want a cure I will come back to the white mage. If not, I know how to use Potions, Dusty Elixirs, and Convert/Manawall/Manafont/Manawell to my advantage. In that kind of situation if I die I only blame myself.
I was referring more to a certain white mage level 70+ I know who only cured himself once an entire 3 hour long GoV party. Of course he died several times as well as the rest of the party. This is an example of a leech healer.