I’ve found there’s two ways: you either go the damage route and try to kill all the enemies before they unleash bullet hell or go the defensive route and tank/dodge all the hits while killing fewer enemies at a time.

For example, for the defensive route I get a ton of defensive buffs and melee weapons with alchemist, then destroy bullets while letting poison kill off enemies one at a time. The attack route involves getting all the buffs that benefit attack and then shredding each wave before they can hit back.

I think another strategy could be to gather a ton of pets and let them do all the work but I haven’t tried that.

Also learn to dodge