A while ago I did a test on how it is to only heal an expert dungeon as WHM. I was active 17% of the whole dungeon (while the rest of my group members were active 72-77% of the dungeon).
The only things I actually cast during fights in the whole 21 min Xelpathol were 16 Medica IIs. That's less than 1 cast per minute. Everything else in my healing was instant abilities (Regen x24, Asylum x7, Assize x4, and Tetra x4). I also cast Cure II but only 5 times in the whole dungeon and they all were cast between pulls, not during them. Here's a video of the boss fight on that run:
https://www.youtube.com/watch?v=jBgM...tu.be&t=17m17s.