AHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAH :)
You were serious ?
AHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAH :)
Even a BRD will do more damage.
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I don't know about doing more DPS than a SMN (though it wouldn't be too surprising if the pack was rather large and died quickly) but MNK can certainly put out solid AoE numbers with Rockbreaker and Arm of the Destroyer. The potency values seem small, but in general MNK has low potency skills and yet it's the king of single target DPS. Why? GL3.
That said, BLM will always reign supreme as the incinerator of trash mobs. BRD will be right up there as well due to being great at spike damage with the numerous damage buffs it has, as well as the AoE spam.
For speedruns, if you get a solid MNK in your party, any time you lose on trash pulls you more than get back on the boss fights :P
It's true you can't burst without stacks of Aetherflow, but please don't discount Energy Drain. Sometimes stuff needs to die quickly, and you don't have time to DoT it up and Fester. In this scenario, you can alternate Ruin2 and Energy Drain. This is for stuff that needs to die super quick but doesn't have the HP/time to justify full DoTs.
Personally, I use BLM or SMN depending on the fight and preference at the time. I prefer SMN whenever possible, but sometimes BLM makes more sense (or, you know, I feel lazy...).