The biggest problem I have with the shadow world is that it seems to overturn all the party building that has been done before that point.
If a party members will be separated at the beginning of the quest, with no way to communicate with each other for the majority of the quest, what is the point of building a balanced party? If party member cannot meet each other until the quest allow them, why not just sent 4 random people into any shadow world since they cannot work with each other anyhow?
Even if the party members must be inserted into roles in the quest, the party needs to at least be able to choose who will take on which role, and how the ability of each member can be maximized. As it is, what or who decides the role each party member will take on? If Romantica took the role of assistant, she will butt head against the chef for sure and not get out of the kitchen at all. This shadow world story is turning into a visual novel game, which is against the whole scheme of the story.
I can see several ways about this. One is, the "power behind" wants the quest to be completed so no matter who takes on what role, the quest will be completed. Two, it is random, and if the wrong people get assigned a role they are bad at, the quest will fail. Three, the shadow world want to trap the people inside, so it will assign impossible roles like being vagants to the players so they can never clear the quest.
Being assigned a pre-determined role in a quest is just so wrong in a story that is supposedly about showing the bad part of having pre-determined roles like alpha and beta, nobles and commoners.