well yea but theres no way a player has any idea what the parry is and how to effectively perform it at that point, it is literally not mentioned. I knew about it bc i read through the entire manual when i got stuck.
you dont need to balance the first boss to be hard on subsequent playthroughs. if anything, you should design him to be a pushover when you are more fluent with the mechanics.
since many other aspects of your game where awesome (mainly the presentation, visuals sound and such), i would suggest next time to try getting into playtesting, it really does help a ton.