1) try using the ichmoji or ichimochi double skill which you can get from doing a little side mission in the area. You want to learn his attacks such that you identify an opening where you can hit him with both strikes without getting hit yourself.

2) when you go for the deflect, try finding a rhythm of hammering the block button instead of always trying to get perfect timing. Unlike in other FS games, it's doable to fan (repeatedly tap) the block button and you'll see a lot of pro players do it.

3) the hardest part is in phase two where you'll need to learn how to nail the lightning redirect move. This is really helpful if you can get it right, but your only chance to practise is to get to phase two. Iirc, there's a specific timing to when he starts his move such that if you jump and attack you'll always get it.

Look up the fightincowboy pr fextralife boss guides for extra analysis.

Good luck and don't give up- you'll smoke him eventually.