open world dungeon mustn't and aren't the solution is worst actually, open world dungeon lead to abuse where people stay to a spawn of a monster for X time for get what they want. at the end is not anymore a dungeon, people farm one place in the dungeon and is all.
we mustn't look into past for find new solution but really in the present.
so far what are the trouble with the dungeon we do have in mmoprg:
- they are linear!
- they are unchanging, means nothing inside change from one runs to another.
- they follow the same rule, meaning: Trash until we reach the first boss, then more trash until the second boss, rinse and repeat until last boss.

what need to be changed is to change this 3 point.
make the dungeon, less linear, less unchanging and more important make them different, not forced to be a rush throught trash until the boss... it's a lazy way to make dungeon!