Stop comparing Luffy with others
Luffy has done stuff which yonko haven't even
Only Kaido has escaped from prisons
Did Shanks escape Impel down? Fight WG? Is he a D? Etc...
People get higher bounties based on different factors
We know Oda has been highlighting King's race and him being a calamity/disaster (barbaric/torture loving pirate) even Zoro called him a massacre soldier.
So far Oda focuses on King's race that even wB called it race of gods, why Linlin wanted him, why Queen hypes their fire...
How Oda wrote and hyped each :
King : mainly about his race
Marco : mainly about his regen
Katakuri: mainly about his own strength via haki mastery.
Nobody brings up Katakuri or Queen's race, same way nobody talks about Marco being super great in haki and power like kata was hyped , same way nobody hype Kata for being smart like Queen or Benn.
King fanbiys wanna create some fanfictions. If you want me to believe His race and being barbaric doesn't play a huge role then then Erase all the hype King got for his race.