A:) Has Zoro taken worse damage than what Killer landed on him ?
He has, against Mihawk and Kuma. But both those times, even if he didn't fall unconscious, it doesn't really matter since the damage each of them did to him respectively, was far greater and lasted far longer from arc-to-arc with Mihawk actually scarring Zolo.
B:) Luffy told Zoro all the animals in the region are poisonous so he can’t eat anything (including the water)
Yes, that was part of the joke was that Zolo ate a bunch of poisonous food and didn't get sick outside of mild stomach ache.
The fact that Zolo didn't even know he was poisoned to begin with shows how little affect it had on him, let alone 9 days later which by that point should have been filtered out.
C:) We understand the same day Luffy arrived is the same day he gets knocked out by Kaido
Yes
D:) Databooks confirm Zoro has been wandering Wano and has been fighting constantly
Also yes
E:) Since Luffy arrived in Wano to the fight with Kamazou roughly 7-8 days has passed : meaning Zoro has been wandering + fighting with no food or water for that duration
So Zolo's been fighting fodder for a week with 0 food 0 water, still doesn't compare to child Sanji going 75 days with 0 food 0 water.
So by blaming Zolo's unconsciousness solely, or even majority on hunger your basically saying he is too weak to endure a mere week of no food no water in a world like One Piece where a child can endure over 10x as much.
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It's most likely the only feasible explanation because he proved how much blood he can lose without going unconscious back in Thriller Bark. Basically the reason why he fell unconsciously has to be mostly related to his hunger and hunger probably didn't kick in immediately but was a process.
Not a good comparison once again Thriller Bark he was physically and mentally prepared to take in Luffy's pain, he even had a sample of it before doing it. Kuma even warned him what would happen before he did it.
Against Killer, it came in a much faster and more unexpected succession. He had 0 time to prepare physically nor mentally. Had he been prepared he very likely would have been able to endure it much better.
Not only that, but it's also a bad example because Thriller Bark left him wounded over an arc later in Sabaody, where he could barely fight the Pacifista without losing blood and becoming exhausted.
Compared to this? Sure he fell unconscious but he recovered less than a week later.