Not every coc wave is the same power. Shanks did a little output in Whitebeard's ship, here he obviously made it stronger to reach Wano. Mihawk isn't scared of Shanks's coc. And GB isn't only scared of Shanks's coc dude can you even read ? He got ready to gtf outta wano when he learned Shanks and his wrew were there and wasn't ready to fight them.
Mihawk isn't afraid of Shanks's entire crew, and Shanks was a yonko during this exchange.