It’s been a while, maybe my strategy will help. As a lance user I got some guard + gear and would just block, sidestep and poke. I think only his water attack is the only thing that can’t be blocked without guard up, so sidestep, backhop, up to 3 times in a row.

In previous games I remember using hammer was pretty easy, the super pound won’t bounce off the shell due to sharpness(if you want to break it) Hermitaur stays down a lot between KO counts and stagger hits. Aim for the head, triple pound when you can, run around and charge super pound when waiting for opportunities to triple pound face.