100% typically means full completion. Yoshi's woolly world draws a very clear line for what is cleared and what is not, with yoshi doing a dance and a stamp being added to a level when you complete it, and a star being added on the level select screen. When you collect everything collectible in a level, a star is added to your SAVE FILE, giving a pretty clear hint at what completion stands for. In the original Yoshi's Island, full health was required as well for 100%, although for different reasons. Overall it makes no sense to not get health for 100% as you are literally not collecting and completing all that the game counts for completion.
I'd vouch for 100% no badges as well, it definitely seems a lot more interesting than what badges can provide, and believe me, I've tried to use badges, and they definitely only make the run easier at the expense at what makes yoshi interesting and fun. It definitely has the highest skill ceiling and allows for most interesting stuff. I also don't quite see the problem with adding it, any% has a no badges leaderboard and I don't see why 100% can't have a main leaderboard as well. If clutter is your problem, then legacy categories like pre-usa 100% or "All Collectibles" can be taken off.
Yeah it makes no sense to not collect hearts for 100% as its a legitimate game collectible that counts towards your completion, see no reason why that wouldn't count.
I agree and don't think we should have a no-oob category.