Insane mana drain in Simulacrum Pinnacle Encounter

I just don't get why it's there. Mobs are tanky, you're facing dual bosses and multiple rare packs of mobs etc etc.

Why is there an added constant mana drain on top of the whole area?
Isn't the blue mana drain circle mobs enough?

Spamming the mana flask and still draining out on every single attempt, I have both mana leech and mana on kill and never had mana issues on this character doing any other content.

Please for the love of Jebus GGG.

I just got wrecked by a Mana Siphon elite in the third wave of T3 Simulacrum. Hours to gather 150 Splinters only to get destroyed by RNG in less than 5 minutes: I couldn't outrun the Rare (because he was faster than me, even with my +39% speed), I couldn't stand toe to toe against him because of the other mobs that kept spawning, I couldn't oneshot him fast enough with my Mana Stacking Sorceress (because if I'm unlucky enough that my Arc damage roll fizzle, I then have to generate new infusions in order to have a chance to actually hurt the enemy).

I can't stand these fights where no strategy is viable for my character.

Like I said many times to this day, a game that needs to leverage these player's agency negating mechanics in order to beat the player is a deeply flawed game, from a design perspective.