let be honest someone like Mihawk wouldn't naturally join Buggy... unless Buggy acts like a cover to him since Marines are after warlords..
But damn Buggy is a genius if he managed to get someone like MIHAWK... MII FLIPIN HAWK under him
Mihawk joining Buggy makes 100% sense imo
he doesn't enjoy fighting weaklings all the time, so if a bunch of shitty marines keep coming at him all day, it would ge tiring
by joining Buggy and turning him into a Yonkou, Mihawk can just chill and only fight if they send actual threats, like an Admiral
so it's a win win for Mihawk
he gets to chill against the shitty enemies
and he also gets marines attention to send Admirals after that Yonkou crew