To be fair, they have been recovering for over a week before Green Bull even arrived. Luffy and the others were also portrayed like they were all healthy again, so I assumed it would be a similar case for King and Queen especially with their Zoan recovery.
Yeah Green Bull can't neg diff YC1/YC2 at the same time if they are at full health, but that still doesn't mean they can defeat him even if they were at full health.
They would still get defeated regardless if they were nerfed or not.
We also can't forget this quote by Green Bull.
Either way I still think it's weird how Luffy and the others are portrayed all fine and super healthy meanwhile it is the opposite with King and Queen, then you also have that one chapter where Luffy and the others were all ready to fight Green Bull.