It's becoming increasingly clear Shanks and Mihawk are the middle generation versions to Roger and Newgate.
-Roger was the Pirate King while Shanks is an Emperor
-Newgate was the strongest man whilst Mihawk is the strongest swordsman
-Newgate and Mihawk had the opportunity but then denied the chance of becoming Pirate King and Emperor respectively
-They are rivals, but have a strong respect and even amicable relationship
Even the difference between their bounties are the same at approximately 500m.
And just as I predicted, Crocoboy prefers working in the shadows. He didn't necessarily want to be known as the leader, and even prefers Buggy get the shine if he can continue to enact his plans with as little attention on him as possible. And good of Oda to make it clear he and Mihawk run this gig. They'll surely spice things up nicely now that they are independent agents from the other superpowers.