And I should have mentioned in my first comment, props for trying to recreate Sekiro's combat from the ground up. To be honest 3D action combat is something I haven't tried myself, mostly due to the issues you clarified above.
It's always been a little daunting for me to try to worry about syncing animations, hitboxes, damage/motion values all in one, so I've never attempted to build any 3D games with combat like that, so I can only be so upset about the issues that I raised in the boss fight, when clearly they're already things you tried to consider.
(And I will admit I definitely did brute force that second level, and barely looked around for other paths, I was actually laughing at all the projectiles myself, when they were flying past me into the skybox)
But thanks for the detailed response, sorry if I came off as a little rude, and good luck on the long term project!