Yep, must be The Hack, then. Not entirely foolproof, or at least used to not be, but pretty mandatory. It is quite doable in other ways as you've said. And it's not the only boon from that particular deity that I used to rely on there.
EDIT: Come to think of it, that dungeon really opened my eyes concerning the other boon back when you had to think about dealing with Bleaty and Thomity.
And Namtar's Lair was always my least favourite one, I always considered if excessive. Quite possibly due to my preffered playstyles though, it really throws a curveball (pun intended) at some of the obvious roflstomp strats.
Say, while were on the subject, as far as I recall some of the vicious dungeons have no proper subdungeon, or have had no (Dragon Isles, Naga City as far as I recall). That alone made them quite a bit more difficult than regular levels, whas this ever changed or not?