Dhoulmagus is definitely a pain.

When I had gotten to him, I was in the 26-24 level range. I took a couple of hours to level, though only reaching 28-26. I just kept at it, and eventually beat him.

Also, Angelo learns Multi-Heal at level 30.

Not much help, I know, but you really just have to stick with it, or bite the bullet and fight to level up.