Best Job / Class for AoE Killing lvl 45+ Mobs

[BlueMage]

he's looking to constantly pull huge packs of mobs though, a blm would fold like paper

BLM survives fine and things shouldnt be living long enough for it to matter. He's not pulling a raid boss.

Is SMN better than WHM or BLM... if so, why is that?

You can just run around mindlessly DOTing up everything.