If you are struggling with boss fights, here are some tips.
Defeating Boss Tips
Easiest for the boss fight. Sucker punching still works. Just rush in and cross cuts to his face. For the final unarmed stage, up+Y can reliably one shot him.
He’s pretty fast in parry riposte so you can actually trade blows with the boss. His down+right+B and down+right+A can hit him with some reliability when used in primo tempo, that is, execute the move at the exact moment when both of you are stepping closer to each other which just made yourselves within the range of your attack. Note that his down+right+B has some insane range.
Long guard+thrust in primo tempo works pretty well. His thrust can sometimes hit 2 times in a single motion and that might bring him down quicker.
Do not attempt the boss fight with Isabella. Somehow they made him a giant when you play as her and his saber is longer than your longsword.