If you do it in ilevel 65-70 average gear then the fight is a decent challenge but nothing too tough.

But if you did it with mostly 70-90 gear the fight is no challenge at all, it is almost completely trivial.

You can't compare it to other endgame because Ultima HM is designed to be doable with terrible gear, so having decent gear makes it extremely easy. Since it's a lot harder to overgear coil and extreme modes unless all your gear is 80+ with mostly 90, they are still challenging with decent gear.