A lot of the mechanics here aren't fully laid out progression wise. This build was to demonstrate metroidvania progression and map tracking as well as a few other things. I do need to think about how I want to have the player slide down and not get in the way, as you said. Currently it's just a Kirby implementation. Maybe I could do it with a double tap? Idk how players feel about that.
Rolling increasing your jump distance traveled is going to be a feature because that momentum is too much fun. I love how much it breaks things, so I am debating if I should tell players about it in game or not. Airdash is meant to navigate tight areas like that spiked room where the spikes are also on the walls. There will be more sensible progression with navigating rooms with which ability needed, promise.
You speak about how movement should be like breathing and I 100% agree. There's one bit for example where the wall jump halts momentum sometimes and this bug has been infuriating to figure out along with plenty of other bugs that have still been consistent (spamming projectile will lock the book for example. STILL IN THE DARN GAME AGH). It's currently just an issue with the way I have momentum interruption handled so it is something that will be addressed over time.