I doubt luffy's endurance grew so much from the time hody bit him and ceaser knocked him out till when he beat katakuri. its simple , the plot needed both of them to be alive to eliminate their threat, once they do they can pass out. luffy wouldnt fare as well if katakuri didnt also put a jab through his chest to even up their fight. killer did no such thing .
but luffy is >
just not as much as people are suggesting. certainly not two times as strong for people referencing ennies lobby