while it would be nice to have a hard dungeon that is not part of the main story there is a reason we can't have nice things.

lets take "The Steps of Faith" for example which when it first came out it was pretty hard for a DF group that refused to work together, which got the hell nerfed out of it at the communities request. the other issue was that it was part of the story

I fear that if SE release anything even a tiny bit hard in a dungeon it will get the crap nerf out of it by community request since no one will do the content.