As soon as the ranged/OT can kill Bennus on their own, it's best if the melee don't touch 'em (except to prevent an awkward phase change). Motion is usually a DPS loss for melee in practice, and it doesn't take maximum advantage of damage-type debuffs like Disembowel.

Ninja and monks have a good mid-way option in putting Shadow Fang and Demolish on Bennus, but dragoons really lose that "perfect rotation" if they try DoTs on Bennus due to the 1-minute respawn time and the 1-minute DRG rotation.