He's already near Mihawk
Having superior skills and Haki than Vista (high high tier) who can rival Mihawk's skills
DR Zoro (upper-low high tier) was already a WSS candidate. Wano Zoro is near WSS level!
He won't fight Mihawk again!
For Mihawk to be a challenge, he needs to Join a Yonko or rejoin WG. If he joins Shanks, the battle will be friendly.
It's already a friendly challenge since they spent 2 years and bonded as Student-master
Zoro will be WSS after beating Shiryu or Fuji.