I think trivial categories should be kept. Like the category 'Song with no drag notes on Easy', that could be unecessary, but it could be worth noticing as a trivia. Which you all think are useless, I think they're noticing for some certain people, or some others might just for fun but not reflect the game, keep them.
And about the category with multiple authors, I think you can add all Eyemedia, Rabpit, MILI, Baroque, Alpha Legion, Project Grimoire,... After all "multiple authors" means the songs have been composed by many people. Cytus doesn't have too much of them after all.