The hammer will actually show you the note that it's going to change to (you'll hear a sound effect, see the hammer bounce and at the top it displays the note and its appropriate cololur), apologies if that wasn't made obvious.
Definitely thinking about balancing the fight though. Thank you for the feeback.
Viewing post in Chapter 2's boss level is unfair.
It's a bit hard to watch the in-game cues when you are also focusing on trying to hit the notes properly as they come at you. So I can see people knowing the cue exists, but not being able to see it as they keep trying to hit the notes, or they don't know that the cue exists because they are trying to hit the notes and focusing on that rather than the background.