Honestly, updrafts are doable. The main problem here is when you are unlucky enough for the rift to not bring down Mordremoth’s blue hit bar in the last stretch. The rift doesn’t stay there for you to try again. Instead it disappears and Mordremoth stays invulnerable to your attacks, forcing you to kill yourself and start from the top of his fight.
I don’t mind difficult fights and I appreciate that his is so challenging, but to be halted by an action that isn’t doing its job is annoying as all hell. This is especially true because you have to rinse and repeat that for the whole end, and one flub on that is intolerable.