Honestly, I think the Dreamworld is a good idea, but very badly done
There's a lot a of setup, but nothing happens after the first few nights, and MC never truly tries to explore the iron doors stuff
The whole martial artist organisation is very bland too, it's supposed to be a big organisation and all, but we never see them actually do something, and it makes the MC work as a rookie after 400 chapters
Imo, it should've instead be the MC working as its own faction, focusing on demon hunting and investigation of the iron doors, while keeping contact with Gracia as it's the only relevant character with Zero in here (except maybe the Master now I guess)
It would remove the martial artist organisation, fix the pacing by making it a easy excuse to put more exciting stuff in the middle of peaceful times, and develop the ancient witches more as they actually do stuff in the dreamworld
But imo, it feel like ever since the MC won against Zero, the story kinda lost its fuel, as in the chapters feels less interesting
I mean, it's still very good, but really not as much as before
On another note, it's annoying how the author still doesn't want to make a choice about MC and Nightingale's relationship, I can't fully appreciate either Anna nor Nightingale romantic moments with MC when I know that Nightingale will always feel sad afterwards, it's been 3 years since MC met Nightingale, the author should've make a choice to either make it an actual harem, or make Nightingale actually move on with her romantic feelings about MC