MSQ

[Seraphor]

Exactly!

So why are they required for the MSQ?

...I think you're getting entirely hung up on the arbitrary naming of the roulettes.

Those dungeons are required for the story... because they're part of the story.

MSQ Roulette is just the name of a roulette... and roulettes aren't part of the story... they're a tool for getting people into queues.

This is a story driven game, everything is part of the story unless it's specifically a side quest that has no consequences on the rest of the story.