/WHM (but /SCH is a perfectly valid alternative) was my subjob of choice on RUN for a large variety of content but if we're talking about recent ones I could list 8 Sortie bosses with Mage setup.
In Sortie you don't need to supertank, as such you don't need the boons from /BLU (mostly cocoon and AoE tagging).
To be fair, /WHM can be perfectly fine for tagging as well, you have Diaga and Banishga.
Can heal yourself and others just fine with a decent Cpot capped DT midcast set. Not that there's much healing involved in those sortie runs tbf...
It's also nice for sneak/invi and for -na