the thing w the shanks mihawk duels are that there was no winner before, and now that shanks lost his sword arm it wouldnt be fun either way for either person. if mihawk wins, he doesn't get to feel like he won fair and its embarassing. if mihawk loses or draws, it means shanks was holding back on him and its embarassing. so they just dont do it anymore.
the question of who is a better swordsman is still up in the air. the main thing that separates shanks and mihawk is not strength but influence. shanks is a yonko with territory, one of the strongest crews in the world, influence with the government, etc. mihawk has a sword, a raft, and an island. thats it.