Yeah, I've complained about Labyrinth before. The mapping algorithm basically creates one long snake with a few minor branching dead ends. Your spawn point clears out a large area in the center and the idea seems to be that this central confluence will give you a choice about how to explore. The problem is that sometimes the spawn area only clears out a self-contained loop and you end up with 75% of the dungeon being just a long hallway. Rex isn't even the problem anymore. You lose the game the first time two strong monsters appear without enough space in between them.
I feel that Purist runs in this dungeon are too luck dependent. I'd like it if some of the monsters dropped those goblin mining bombs.