Technically BLM only has access to Fire (Flare) and Ice (Freeze). THM has access to Fire, Ice, and Lightning. I seem to remember the first Class Quest text explaning the reason why they focus on those elements. Honestly, I've been a BLM for as long as I've been a WHM and I still have no clue what the BLM abilities are about. If you went by the Job Quests I'd be summoning Voidkin to do my bidding like a Warlock or something.
