I wish I could like this comment more than once - while the thoughts were unsolicited, they are much appreciated! I join game jams because I enjoy the process of creating things, and the jam format makes it a great communal learning experience as we all have our unique perspectives to share! To that end, people sharing their feelings on how each component made them feel and what they'd like to see is gold to me.
While I'm very happy with how the game came out, I think you're onto something with the idea that it's "hard but easy" in the wrong sort of way. I could go into why I made each choice that I did, but ultimately it's just "developer skill issue" - I took on a hard challenge (as a solo programmer, did a project that was intentionally mechanically simple to force myself to improve at art, music and narrative design), and could only put so much effort in so many places. I learned a lot from it, but I also didn't have time to fully realise a lot of those ideas, and made a lot of beginner mistakes (audio-wise especially) along the way.
What you mention about the final boss is 100% by design - I wanted it to be something crazy but also feasible, and quickly gravitated towards the circular inputs since they look tough but once you get them down and know they're coming, you can roll your hands over the buttons in a smooth and satisfying way. And the entire fight is designed to show you what the boss can do, before throwing you into a long section where you need to combine them all at once (first the quick inputs from the intro, then clockwise circles, then counterclockwise circles, then semicircles, then all three circles, then circles with surprise quick inputs, and finally the two-line finishers which are also just circles with more A/B presses on the end). And funny you mention fighting game combos, I originally intended to animate the captain's circle attacks as a grab (and the quick ones as a sword strike) after coming up with the input since it reminded me of the usual command grab input. That level of buildup isn't really present in the other bosses - the first one is intended as an extension of the tutorial to get a feel for what the game has to offer, while I focused on the interaction with the parrot for the second one (which was actually developed last), and I simply added "the first enemy's attacks, but slighty longer and including left/right inputs as well as up/down" as the "filler inputs" in between sections of dialogue and flurry attacks.
But I'm glad you enjoyed the game overall, especially coming from someone with such a strong entry!