So Half-illithid warlock Tav + storm cleric Shadowheart + Minthara hits like a truck apparently. Everyone has initiative bonuses, so first turn Minthara hastes Tav, Tav casts black hole to cluster all enemies together, then Hunger of Hadar's them, Shadowheart then calls an upcasted Call Lightning with divine strike and obliterates everything. You can delete half the health of almost all the enemies in the first round if you get lucky, and they all get severe movement penalties from the black hole and hunger of hadar. Plus Astarion multi-classed rouge/fighter/gloomstalker with action surge and crit bonuses can pick off like 4 enemies in the first round too. Then Minthara smites the survivors into oblivion.

Fun times.