Shank equally clashed with Whitebeard, the after effects of which split the sky in two.
And not only does Mihawk obviously not have Youkou-level leadership, he doesn't even have Youkou-level fighting ability, seeing as he couldn't even scratch Jozu at Marineford.
In One Piece Chapter, 1025 Luffy will help Yamato as well as Momonosuke.