Thanks for playing! Jump has a smaller buffer than attacks ( 3 frames for jump input presses, 6 frames for attack input presses, both durations extended by the amount of hit stop freeze frames), but it has one. You're correct that it doesn't respond to being held. I'll experiment with more lenient jumping. Did any other actions stick out to you as unresponsive? I'm aware of the overly strict neutral attack inputs being a problem as well.
That enemy has been a big problem for players. I wrote up some example strategies in another reply, but an information gap is the main theme of the feedback I've gotten so far. I'm working on an update to fix hiccups with the controls, adjust the attack pattern on that enemy, and provide a basic overview of the mechanics in the move list. I appreciate you flagging this stuff for me!