Thanks for all these responses, everyone. I'm glad to hear that the 50-60 dungeons aren't necessarily representative of the 60 AST experience, so I'm going to stick with it.

Lots of you recommended staying in Diurnal Sect most of the time. Full disclosure: I haven't been doing that. So my own inexperience is a big part of it

I hadn't been using Aspected Benefic much. I didn't realize that Regen effects can make such a big difference on the ease of moment-to-moment healing. I'll definitely start incorporating that.

Reading these responses has been inspiring, especially since it sounds like the learning experience isn't dramatically different with WHM and SCH. I'll stick with it!