Imagine being an emperor with the sun god devilfruit, having a fleet of 5000 people and a former shichibukai and the only person who can read poneglyphs in your crew and STILL having a bounty equal to a captain of a crew of 30 metalheads.
I guess Kid and Law aren't considered emperors due to their weak crews. Compared to Luffy's crew, outside of Killer in Kid's crew, the rest are fodder, to the point Oda didn't even bother make them relevant in the Wano war
And it's most likely the major reason why Buggy ended up being one. His followers were hyped by Whitebeard preskip
So it was a logical perspective from Oda's part that he'd develop it further to maintain the running gag of Buggy finding an alternate way than individual power to become a top dog
Kidd Luffy Law having the same bounty is actually quite smart of the WG. The public don't know - and the WG don't want them to know - that Luffy is Nika, Joy Boy and a warrior last seen during the void century.
This way they cover up Luffys deeds just like they did when he beat Crocodile and Moriah in order to preserve the notoriety of the Schichibukai.
At the same time they can't cover it up totally this time because Apoo sent pictures to Morgan. Otherwise I'm sure they would have claimed that Kaido and Big Mom took each other out while secretly going after the trio without the public hearing about it.
But this way with equal bounties they att least make it seem like the trio took down the yonko and thus they cover up the return of Joy Boy.
I love this, it really does feel like Croc is coming.
Crocodile: "Hahahaha, I will slowly starve this country in order to gain power, and make it a famished, drought riddled wasteland in order to turn the citizens against the... leadership..."
(Stares at a barren wasteland full of poisoned water and little food)
Crocodile: "...Damn, Kaido really did a number on this place. Ain't no water to suck up with sand. Fuck it, I'm out."
Let's think about it two seconds : They had seven days to recover with ancient zoan. Jack and Ulti came back within a few minutes of getting getting knocked out. . Also the WG guy was legit for the Ryokugyu vs King and Queen stuff.
The idea they re somehow half-dead is a desperate last attempt at coping.