This method of clearing is a desperate attempt, but it worked. This strat also works on Challenge Mode.

Istina and Greyy makes possible slowing in an area, reducing the chances the Ergate Leaders can slip through untargeted. Eyjafjalla's S2 adds more high AOE damage, with another Caster (Amiya) just in case.

Silence's drone is very nifty in extending her healing range. SilverAsh's S3 is used to clear the Agents sneaking from behind. Myrtle is the DP generator, and for the bait, I used Skadi due to her high health.