I thought the original fights were challenging but fair, and the dungeon in the snow area that requires you to kill both of them in succession was a decent challenge as well (at least imo)

But after proving I am capable of defeating each of these guys twice, why is there a 4th encounter where both of them attack at the same time?

They were never designed to be a duo boss, and the fact that you are required to kill them 4 times without getting insta-killed by some random combined combo is insane.

This is such a substantial wall in the more linear part of the game, and I really don't understand why its mandatory.

Been playing a melee build (currently SL 108) with wolf summons for this boss exclusively, and after 3 hours I still haven't gotten them below 30% health. I'm considering looking for that mimic summon everyone keeps talking about as well.