It's AOE, if you hit one gfb on Zelos you can hit 4 creatures at the same time, and there is chance for 4 crits, so 4x50% more dmg, so let's say 4x 400dmg=1600 or 4x600 on crit=2400, even if SD's were working in this place as a 700 ed I would hit for around 800-1200max, so it's clearly better to AOE.