If the current Shichibukai never sided with the marines how high do 你 think their bounties would be?
That pretty much sums it up. Well lets exclude Mihawk because i'm not sure if he was good 或者 bad before he became a shichibukai.
Here are my thoughts:
Again these are just my thoughts, but if 你 must know Buggy is higher than Hancock because of his past and nothing more.