unkillable harvest monsters

Normally I melt harder Bosses down. My Character is still in progress. But this?!
A unique monster which spams masses of rare monsters which spam monsters themselves and different curses and immunitys and leeching and and and. Full Screen filled with yellow monsters. My Char does 400k damage wwith five Lightning balls for the moment. My longest run there was near to ten minutes and I wasnt able to reach the Unique Monster one time. T12 Map, nothing special juiced - WTF?
For my taste and my normally very strong Character this is not just only a bit over the top and far away from challenging or fun.

You found one of the bosses. There's 4, if I remember correctly.

You need to have much higher dps to stand, otherwise the lag is so absurd that you can't even try to fight.

I could win 3 times and lost one. Not impossible, but not playable without massive dps.

In my opinion, the boss should be reworked (like harbinger, p.e.).