BLM Fire II incredibly lack luster

[Kevee]

320 divide by 3 = 106.6 DPS per mob for Blizzard II.
260 divide by 1 = 260 DPS per mob for Fire/Blizz rotation combo rotation.

Over a period of 10 seconds:

1066 DPS for Blizzard II spam on 3 mobs
2600 DPS for Fire/Blizz combo on single target, hence the only time AoE becomes efficient is when there is more then 5 mobs as smashing down 3 mobs with single target DPS is more efficient and faster then AoEing.

DPS/Mob doesn't mean anything when you're AoEing, as long as the DPS total is more than your single target DPS. You should be comparing 3200 to 2600, with at least 3 mobs. You're not doing 106 DPS with 3 mobs, you're doing 320. You're doing 106 to each individual mob, but no one cares about that when you're AoEing.