Well you're meant to pull and nuke the bugs out together, but not stand still unless you're aoeing ofc. You should have Crucify, Heaven's Edge, Lightning Blade, Magic Arrow and Multishot to cover the bugs when they spawn. They'll spawn 5 each wave twice before Gargoyle goes airborne again. Group what you can and kill it, let the melees cover them once Gargoyle is airborne again.
As for the aoe attack, it bounces, so spread out from his primary target.