I'm here to watch the mega cute Jester and all her cute art.
The Knight plan is... kinda weird...
how does keeping people out help find the traitor?!??
since they would be seen as "expendable" to most who don't know aka "only there to fill the numbers" they were prob made to go in amongst the first ones. the mission? find the crystal and destroy it only after that come to the boss room. the presence of the crystal makes the dungeon act in unnatural ways as described previously. so by staying at the boss room they are preventing a lot of unforseen circumstances. there's also the chance that the guild has some sort of investigation tool to use on the crystal. so the person would prob try to cover their tracks.
a) if the person who made the crystal goes for the boss room first( to cover their tracks with the crystal and claim that the boss started wandering around the dungeon and they had to defend themselves) they will be there while the monsters are still going wild and will need to go to the boss room.
b) by knowing how large (prob an estimation from his gamer days) the dungeon is (aka how much time it took to randomly find the crystal nad destroy it) he know that if it takes significantly lower then that. means that the one who comes early knew exactly where to find the crystal (even if they didn't destroy it)
c) there's prob a few more reasons but those are the 2 main ones that he needs to avoid