I don’t like this idea because your really just beating the game with like a 2 minute mini game at the end

You cant really say "If this... then that" without giving reasons to why you think a category should be added. Star% is completely different to what you call Balloon% and share no similarities. Star% can be finished well before you complete the game, hence Bruncheon, for what you call Balloon%, it would require you to finish the run just to unlock luigi (any% then luigi in mushroom), and now the minigame requires you to connect to online servers which are now paid servers, so no.