Thank you for playing! I appreciate the feedback, and I am happy to hear that you enjoyed the visuals!
We'll definitely add some difficulty options to tweak the input window soon. As an alternative to focusing on the music, player attacks are always guaranteed to land to the beat, regardless of whether or not you've timed it correctly.
So if you focus on pressing any attack button right when an unsuccessfully timed attack lands, your next attack will be guaranteed to be on time. If you go into the hub and try it on the dummy, I'd suggest just focusing on pressing attack buttons right when it flashes white after being hit.
This of course is harder to apply for other mechanics such as the quick rewind and parries (for which there are also some neat tricks I outlined in the game page you can apply instead), but I've found it to be a reliable way of making sure attacks land on time.