He could still fight Shiryu before Mihawk. In fact, it would be more simple that way, we could say CG is like the SH´s second last fight with a pirate crew, instead of the weird mess we have now. The more I think about it, the more I´m convinced Oda was smoking crack with Shiryu. He would have fit better as Buggy´s number 2 since he broke out of impel down and used to work for the government. Mihawks dynamic with CG is a bit forced, with him not really having any good reason to have joined imo.
Well, Mihawk and Crocodile do have a pretty similar vibe/dynamic, they're both pretty stoic and serious most of the time.
Mihawk wouldn't fit in with the BBP because they're too weird for him. There's people who are alcoholic rapists, torturers, mass murderers, etc.
And they just don't seem like people Mihawk would trust or like enough to ally with them.
I mean hell even Kuzan was a little uncomfortable with joining them.
I think Shiryu's the best first mate they can have since he fits their dynamic of being horrible nasty crooks with hax abilities and he doesn't mind fighting dirty at all.
If Mihawk was in there they'd have a lot of problems, for example Mihawk wouldn't be comfortable with sneak attacking Koby and Garp out of nowhere, while Shiryu is probably the one that proposed that idea in the first place.
They're night and day in terms of personalities and fighting styles.