As others have said, a good portion of Luffy's more recent exploits have been hidden by the government. I'm sure his new 400 million is because of his assistance of Whitebeard in the war as we have seen that the WG doesn't want anybody to know about the ID incident.
As for the rest of the Supernova (excluding Zoro), I'm sure Kidd and Killer have killed civilians as well as marines, giving them a boost, Capone seems kinds of ruthless and seems like someone who constantly pillages for money, Drake was a Rear Admiral and most likely has an incredible amount of WG knowledge as seen when he knew about the Pacifista, and Bonney is probably a similar case to Robin as seen when Akainu talked to her. As for Uroge, Law, Hawkins, and Apoo, I've no clue as to what they could have done to receive those bounties aside from basic piracy.
^-"Heck, remember when luffy first met BB? BB did not even believe luffy was worth the 30 mil he claimed to be worth even though at the time luffy had already received the 100 mil bounty."
Actually Black beard was implying that luffy should be worth more than 30 million because he could sense luffy's haki at that time, it actually says haki in the japanese but wasnt fully introduced as a concept at that point.
---------- Post added at 10:55 PM ---------- Previous post was at 10:54 PM ----------
At least that is what the translation available says. I guess it could be wrong although I have never seen a proper source that says otherwise.
they have obtained them reaching the grand line defeating enemies and marines. kidd is the only one,who has got an over 300M, although he doesn't really deserve it,and that's because he has been killing too many citizens. about killer,I don't think his bounty has been increased much for these murders,because he is not the captain. and drake was a rear admiral,then he knows a lot of things concerning the Marine,he is dangerous for that,but he must have done other else.
Actually I also don't get why other Supernovas got such high bounties, especially when Zoro and Luffy were obviously stronger than majority of them and the same Zoro should also had higher bounty than most of those Supernovas.
Remember that on Sabaondy Luffy and his crew took down one Pacifista and started a fight against second Pacifista, before Kuma and Kizaru and Sentomaru arrived, while at the same time Kidd, Law and their two crews barely managed to take one Pacifista. I believe it shows the difference between their powers and their crews on one hand and Luffy's on the other.
I also believe that Drake is surely understimated. He should be obviously stronger than Law and also stronger than Kidd and he also started his New World actions as the most outragious. Also I believe he should have been in the New World as Marine.
I believe that we should consider that Captains bounty increases way more than crew members, so sometimes the Captain's increase reflects all the crew deads and not only his deeds, thus that's why Law and Kidd got such high Bounties. Also Drake was considerably strong even before becoming a pirate. Rear Admiral isn't a joke. Even though he didn't knew Haki to confront Kizaru, but he should have be quite strong with his swords and DF to get such a high position in Marines and of course he grew even stronger, while beeing a pirate, cause he should have fought plenty of times against Marines and it doesn't look like his crew is strong in any sense. They seemed quite average, thus I believe that he was the only strong crew member. The same goes to Hawkins. His DF is quite interesting and he should be really strong as his crew toitally doesn't give any impresion.
I think you are mixing a bunch of things there.... First of all, we never actually saw the fight between the pacifista and law's and kid's crews. We have no reason to believe they "barely" managed anything in particular.
As for the strength of their crews, we have to consider that we have seen all of the bounties of the strawhats while we only saw the supernova ones from the other crews. For all we know bepo was worth 90 mil lol. Of course, I do doubt every single member of their more numerous crews had bounties as is the case with the strawhats less numerous crews but still.
As for zoro and luffy being "obviously" stronger, I would question that a bit to say the least. We are talking about a guy who controls freaking metal (in xmen that guy is an omega level mutant or something), the guy who uses 2 weapons and turns into a dinosaur, a guy who creates a room where he has control over everything, a strawman of sorts (gotta be a strawhat's nemesis or something lol)... Even urouge exchanged a few blows with a pacifista after pulling a master roshi and to be fair apoo's attacks seem invisible or something. Granted that urouge, bonnie and capone do seem weaker than the monster trio however the rest of them seem to have some pretty hax abilities to say the least, I don't think luffy's or zoro's superiority would be obvious back in the day.
Considering that Marines have Vegapunk I think they know the real reach of the power of the Devil Fruits they have. They must use some kind of equation between a regular base of threat base on DF (I see Zoro bounty lower than Luffy and that must mean something considering they both consider each other equals) plus actions taken.
Luffy had a lower DF base, but a high event rate. Kidd has a medium DF with a medium event rate. Caribou has a high DF base with a lower event rate.
There is also a different kind of factor which is direct threat to WG: That implies everything that directly opposes to WG and THAT's measured by power.
The SN that i'm most interested in when it comes to finding out about their journey and accomplishments and etc. is Urouge. Its assumed that he may be from a Sky Island, so his story should be pretty interesting and very different from other "land-dwelling" pirates.
Hmm Urouge isn't so interesting IMO. And from what i saw he doesn't seem especially strong either , i think he earned his bounty the same way as Kidd , hurting civilians and things like that , plus he had the lowest bounty from all the SN so i don't expect much from him.
The one who's more interesting except Kidd and Law and i would like to know how he earned his bounty is Hawkins , i especially like his DF and beside he doesn't seem like the type to kill innocent people left and right without a reason