Great writeup, super interesting to see your development process and overall thoughts.
The 'cuphead' parry (in hindsight, this inspiration should have been obvious to me, not sure how I missed it! :p) is a really fun callback. Imo, cuphead's parry mechanic is quite lackluster: in the context of that game it feels undercooked and slightly out of place. I think you did a much better job of executing on this mechanic using juice + the added combo meter. It's definitely the most fun part of the gameplay loop, and it's evident a lot of care and time went into making it feel great.
Your postjam thoughts really hit home for me. The "not enough playtesting" + "game is too difficult" sentiment is so real. I'm fortunate enough to have someone who is always available to playtest / give good and tactful feedback; I've definitely had moments where I was super excited about showing off some mechanic, and then it just... doesn't work. And it feels pretty awful, lol. Still, showing the game off to friends is the best part of the game dev experience for me, and I'm finding increasingly that moments like these are why I find the whole process so engaging and fun, even if the feedback is really negative at times loool.
One thing I've learned (especially from this jam) is that it often doesn't take much adjustment for something to "feel" good, at least on a level that's good enough. For my submission, this adjustment was the shader effect for the ball that causes it to visually 'squish' in midair and 'bounce'. For your project, I think making the parry hitbox bigger would immediately fix the 'difficulty' issues people were having all on its own (which I see you're already addressing in the upcoming update :D).
Really cool post and game. I will be on the lookout for your future projects, haha. Thanks for sharing!