Killer fought 2 yonko and defeated a pirate dangerous enough to be considered a supernova.
Sanji beat Queen.
Killer should have the bigger bounty.
Killer shouldn't get a bounty for merely "fighting" the Yonkos, just like Sanji shouldn't get a bounty for "fighting Doflamingo".
They were not the winners.
Killer's WIN is against Hawkins only.
What should also contribute for his bounty, is the fact that he's the right hand to Kidd, who might become a Yonko himself (as stupid as it sounds, since kid's crew sucks ass compared to any Yonko crew).
Killer's only good hit on the roof was the "sonic scythe" thing. As pretty as it was, it didn't do more than the scabbards did.
And the "leaders of the new generation" is really weird to play a factor as well, because it's not something from the Government. Is just something that Oden said long ago to Tokki.