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Not to mention Ace was already a famous pirate who was offered as position as a Shichibukai even before joining Whitebeard.
Burgess was completely unknown until 2 years ago just as his Captain.
But it wouldn't surprise me if Oda gave him an Ace-like bounty just to show he is that strong and that's all.
Also, keep in mind that we have seen a swift inflation of bounty. With the new era coming with the "worst generation" aka supernovas causing trouble everywhere, i think there are more dangerous and strong pirates around now than ever. I mean look at Kidd, his bounty is only 80million beli and he is a literal nobody who has only been around for a couple of years.
Yes, i know about the "Brutality thowards civilians" and all that, but i dont think that is quite enough to earn such a bounty. First of all, messing with civilians (robbing, murder etc) is kinda what pirates DO. And regardless of how cruel you are to "regular people" and how many you kill, you would still have to be tough to stay around, otherwise the marines would throw your ass in impel down pretty quick and you wouldnt last in the New World.