I maybe incorrect but i believe, RDM has the highest AoE burst damage as it's possible to put out 5 E-Moulinet 300 potency each with no fall off for a total of 1500 potency per enemy hit.
First off E.Moulinet is 200 potency. Secondly, to do 5 costs 90/90 Mana and Manification. IDK about you, but it takes about 2 or 3 pulls worth of mobs in an Expert Dungeon to get 90/90 if I'm just using Scatter->Scatter. So by the time I get 90/90 from Scatter-ing 3 groups of mobs from the start of a dungeon, we're already at a boss, at which point I no longer have need for 5x Moulinet. Meanwhile BLM is already busting out Flares and Fouls and SMN is busting out Banes/Painflares/Death Flares, melting all the initial pulls of mobs in seconds.