We are forgetting a few details about mages class/jobs.

CNJ - healer, buffer
WHM - healer, buffer, party debuffer, enemy stranding control

* WHM should be a job especialized on: Spirits (ghosts) type, Demon type and Undead type mobs.

THM - nuker, dotter
BLM - nuker, dotter, enemy debuffer, enemy stranding control

* BLM should be a job especialized on: Elemental spirits, and mob elemental weakness.

I'm just meanning that WHM is lacking on spell content like BLM. Yoshi should do a deep investigation on these 2 jobs to balance them properly, making them unique to have in party. Also the concept of WHM been a dotter in the absence of a BLM is also a good concept, but make it impossible to be it in a presence of a BLM. That way jobs rules will not be about multy-tasking.