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