In fairness, I think the DCSS developers agree with you. Branches are for the most part getting shorter (extended excepted). Lair is still pretty long, but I'd rather it was made more varied than just shorter. Hall of Blades is now in Elf, and Elf is only 3 deep. Crypt's only three deep. Depths is actually pretty varied anyway. The main rune branches are all four deep.
I mean, Octopod Transmuter is not... easy... but all the long major roguelikes (ADOM, Nethack, DCSS, ToME) are basically games of patience. They're repeatably doable if you learn all the rules and are careful. Speedruns are harder, of course.
Whereas even if you're completely spoiled and have achieved a perfect score in the past, Brogue is still difficult because every decision matters and you can't take your time. If you don't plan the most efficient way to explore each level then you starve, and if you miss or waste a key resource then you die because you aren't powerful enough. I still love Crawl but I strongly second the recommendation to give Brogue a whirl.
If you ever want to increase the difficulty of a roguelike, you could always adopt a conduct[1], like "foodless", "atheist", "pacifist", "illiterate", etc.
I've done SpEn (3), MiFi (3 & 15), DDEE (3), but I still find the game incredibly hard. I've been playing MfIE and getting wiped out repeatedly before even collecting a rune. And that's _still_ an easy combination.
Brogue does sound interesting though. But perhaps beyond my skill level.
Still rock hard though.