Such a thoughtful review! Thanks so much! I'm really glad you were able to make it to the end. As for the difficulty, I want to keep it hard since some of my favorite games have similar difficulty. But Celeste has a nice option in the settings to enable accessibility features if needed. I think I could add some optional checkpoints and adjust physics or game speed through a setting so that hardcore and more casual gamers could enjoy the game.
I'm really surprised that you found one of the secret areas. Sorry I ran out of time to add something fun there. They will have stuff in the post-game-jam version