Bounties will Tell you ¯\_(ツ)_/¯
Haven't we already learned that bounties aren't a direct measurement of power level
It took both Kid & Law to defeat an opponent weaker than the one that Luffy defeated by himself, while Big Mom was literally standing there and letting them get attacks in...and even then, Luffy's final attack on Kaido was more conclusive than the final sequence of Kid & Law's attacks on Big Mom. Even considering the fact that Kaido was weakened at the start of the fight with Luffy, he at least acknowledged Luffy as someone capable of fighting him 1v1. There's hardly any indication that Kid or Law can last in a 1v1 fight with Big Mom at all, and she's
weaker than Kaido.
And Zoro defeated Killer with
neither Enma nor KoH. Even if you say Killer was nerfed, there's no way him regaining his punishers can make up for the fact that Zoro powered up twice when he was already capable of taking him in a fight.