Wow, thanks for the video! Looking back, that drop room was pretty bad with the enemy placement, especially with the game respawning you at 1 health for some reason. It was really helpful watching you fight the boss, from that perspective there's a lot of stuff that doesn't get communicated. The boss is supposed to follow you until it gets all its attacks out on you, but it just kinda looks like its stuck in the attack phase. There's also no hitbox until after the boss' melee phase is over, but again you'd have no way to know.
On a more positive note, since I did not write it, I feel it's ok for me to agree the music does indeed go hard.