Okay, I recently finished the first campaign in this. My winning team was a fighter, templar, and enchantress. I thought RNG screwed me over with no dedicated healer. But, my templar single-handedly took out the first boss and wound up doing really well. I pumped up his Faith every level, and sometimes contributed to Life, and he got the job done as a tanky healer. The other two did well for DPS and staying alive, and while the fighter's special skills aren't that great, the enchantress' were very helpful, especially the status cleanse one when the templar wasn't able to.

I'll echo what I said before, the two things that take this game down from impossibly hard to perfectly manageable are 1. handling status immunity for each dungeon and 2. having some bit of elemental resistance for the upcoming dungeon. Number 2 goes a very long way towards making sure your healer can do the job, which most of the time isn't healing as much HP as possible, as it is curing all the status ailments your lucked-in-to gear can't prevent.