This might be an unpopular opinion, but I don't feel like they take too long. 20-30 minutes seems fine to me for the amount of EXP I get, or for additional tomestones.
The cap at level 50 also doesn't bother me.

The only reason the MSQ roulette still exists today are the cutscenes. Were it not for those, all 3 dungeons could be integrated into leveling and trial roulettes respectively after the rework. But since they take longer than everything else in those roulettes, leaving them separate is the only reasonable solution.

They should not expand on this though. It's bad design and they learned from it, the MSQ roulette being a constant reminder of why lengthy cutscenes in dungeons are not the geatest of ideas. If they were to expand the MSQ roulette, they would only increase the amount of badly designed, cutscene heavy dungeons from 3 to a bigger number, making the problem worse.