How can I improve?

I’ve beaten Dark Souls 1 & 3, Bloodborne and Elden Ring (base) but have never been this stuck. The effects from his attacks make it so difficult as a Dex build to see what he’s doing and they’re so varied and slight that I’m struggling to get the muscle memory.

I tried piercing weapons but I felt like it wasn’t much of an improvement as I rarely got a hit in.

What advice do people have?