I'm going to admit that I have no idea what you mean by "reaction times being janky." Telegraphs and guard timing are all consistent and working as intended, and that aspect of the game in particular is balanced exactly the way I want it to be after feedback from playtesters.
If it's just that the attacks are too fast for some players to react to, then yeah, I'm sorry about that... I always like to try to accommodate for players of differing skill levels when I'm making games that are meant to be harder, but I ran out of time to include the kind of difficulty options I usually do... Thanks for giving it an honest shot anyway, though!
As for the final boss and ending, there's just one ending that plays the first time you lose, and a different ending if you win