Wasn't Zoro taking Luffy's pain+damage accumulation+fatigue, the exact reason that Luffy was fine the next few days? I'd still put Zoro's pain resistance / raw endurance above Luffy, even if i think Luffy's overall powerlevel is surely above Zoro.
Luffy was fine immediately after waking up thanks to Zoro taking his fatigue. Normally this process takes a few days of being bandaged, Zoro was actively nerfed into the NEXT ARC from taking this fatigue, Luffy recovers between arcs.
Zoro having more endurance than Luffy doesn't carry any water with me if it is SOLELY reliant on a 500 chapter old feat- a feat that can be easily dissected and explained to minimize any gap it would create.
I'm 100% sure Luffy could have accepted Zoro's pain and damage with equal or less repercussions than how Zoro handled it,
still a brave noble act on Zoro's part (mostly pointless in the long run considering Kuma was a double agent and would have just sent them off to their locations to train, but Zoro didn't know that).
Impel Down to Marineford is a bigger damage/endurance feat than anything Zoro has ever withstood:
Being beaten, frozen, bitten, shocked to the point of using CoC, poisoned to the point of fighting on a razor edge margin of death, requiring a long shot magic treatment to survive, draining multiple years lifespan and struggling for hours to recover.
Being stabbed by vice-admirals in cheap sneak attacks, fighting against multiple people stronger than you, get pushed past the point of exhaustion to requiring further drugs to push on, save Ace, get melted by Akainu's serious attack, while prone and vulnerable, having the mental damage of seeing Ace die. Require surgery from Law and be told not to move lest you unstitch your wounds and die.
Strap on some bandages and he is fighting his superior Jinbe.
WCI is a bigger bigger damage/endurance feat than anything Zoro has ever withstood, and more time relevant:
-WCI Luffy recovered after simply having some food and a short rest from being starved and fighting a marathon battle against an army to wait for Sanji-after fighting a YC3 in a multi hour battle- after nearly having his arms ripped off trying to escape the book- after having his skull cracked by Sanji while not using haki to defend out of protest.
-WCI Luffy then fought Katakuri, a superior opponent, for 12 hours while having to grow in combat ability and taking the majority of the damage throughout the fight, against an unhittable opponent, he was drugged and drilled through the organs, still activated G4 and ultimately got up multiple times to win the fight.
Luffy recovered from WCI in time for Wano with no arc crossover repercussions like Zoro had from his sacrifice.
I don't see how anyone can put Zoro's endurance above Luffy based on a 500 chapter old feat that has been superseded by better endurance feats from Luffy.