But royal does way less damage than goring...

also there isn't a single pull where you have to deplete all your mana on flash, you're just wasting GCDs that could be used for (albeit low, single target) damage.

Also if you're chaining flash you're losing mitigation. If you need max AoE you'll want to do 3xFlash > 2xfiller > 2x flash > 1x filler > flash