They are relative to each other but don't you think there's a reason behind Oda giving both these first commanders very similar bounties, a 300 million higher bounty than Katakuri? Especially when Marco's and King's bounties were both released in Vivre Cards and around the same time.
Well Bounties dont represent strength, Marco was a part of the WSM's crew and went to MF as well as the war with BB, we do not know if those two wars inflated his bounty or not.
As for King he is a part of a crew that destroys a lot of shit, engages in chemical viral warfare ,etc
So those two having higher bounties makes sense as opposed to Katakuri who probably spent most of his life in Totland protecting it, heck he isn't even here right now but instead is guarding their territory.
Also you forget that Rayleigh himself hyped up FS users to the moon and so far the only FS user we saw was Kat who had to deal with MC MCplotarmor Luffy bullshiting his way to the win back then.
Anyways, they should all give very high extreme diff to each other, Ill say that Kat would probably lose more often than not given that those two are more resilient than him but he shouldnt be far away in AP ( with his Mogura) and his maneuverability/ Agility should be way higher.