Bounties have nothing to do with power levels and everything to do with how much mayhem you cause. Bart's bounty is huge because he was a ruthless murderer on the way to meet his idol. Same with Kid.
Jack will basically genocide anything in his way which is why he's at one billion. Same seemingly with most of Big Mama's crew, they are just stone cold murderers.
Hasn't it been said before that Luffy has a relatively low bounty considering everything he's done? I mean.
A) He defeated Crocodile (which was hidden by the Government)
B) He declared war against the World Government, defeated the CP9 and avoided the Buster Call.
C) He defeated another Shichibukai.
D) He punched a Celestial Dragon.
E) He is the master mind behind the biggest prison break in Impel Down history (official versions says it was Buggy I think).
F) He was part of the War of the Best, where he used Conqueror's Haki.
G) The whole Dressrosa arc.
If you take all those crimes individually, he should have a much bigger bounty. But I feel like they don't want to give him credit for all his crimes because, honestly. There would be a lot more Bartos if all that information was public knowledge.
Luffy could be a living Legend already if it wasn't due to the government covering up most of what he's done. Most Yonko understimate him because they were on the other side of the world when most of this happened, I think.
Too bad Zoro wasn't there, he'd be halfway to the bone by now.
Poor Nami is always there when somebody wants to cut off some limbs. Remember Little Garden?
