At this point I feel that all 4 player content up to 50, MSQ or otherwise, should be folded into a single category and they should just remove the cutscenes interrupting the content. Push the exposition to after the boss fights.

Things don't need to be removed just because you don't want to do them. You can just not do them. That's fine.

I'd probably suggest that 51-89 all be folded into one category and just be permitted multiple times per day.

I think the separation of the top level into 2 tiers makes sense to not lock people out every time a new dungeon comes out and give them a chance to reach any new iLvl reqs.