Worstgen
Cinera
That's a reasonable take. I do think the knockout needed to happen for the plot:
* Stop chasing Shusui.
* Meet Hiyori and Otoko.
* Witness Yasuie's execution.
* Attack Orochi and clash with Kyoshiro.
* Swear vengeance upon Orochi.
* Receive Enma.
* Stop chasing Shusui.
* Meet Hiyori and Otoko.
* Witness Yasuie's execution.
* Attack Orochi and clash with Kyoshiro.
* Swear vengeance upon Orochi.
* Receive Enma.
Cinera
None of the above would have happened if not for his fainting, and those events are very important for the plot and ultimately Zoro's role in Wano.
Cinera
It was Yasuie's execution that made Zoro swear vengeance upon Orochi (he has stated that he doesn't fight for revenge, so that he's doing it now is important). Yasuie's execution gave Zoro emotional investment in the fight and a reason to wield his blade beyind supporting Luffy. It was at Yasuie's execution that "no one being able to take Kaido's head" was mentioned.
Cinera
Hiyori is Oden's daughter, and she and Zoro bonded. She's taken the role of a secondary arc princess, and her meeting with Zoro has been important. She's the one who contextualised the suffering of Wano's citizens under SMILE's curse, she disclosed that she wanted to kill Orochi with her own hands, etc.
Cinera
Receiving Enma provided Zoro a route to get stronger, but also served the (IMO more important) role of symbolising Zoro inheriting Oden's will (the Editor's note on that panel is literally "inherited will" and it's a major concept in One Piece).
Zoro has also been hinted to surpass Oden and blacken Enma.
Zoro has also been hinted to surpass Oden and blacken Enma.
Cinera
I could go on, but you get the gist. This was mainly my attempt to address you writing off the plot necessity of Zoro fainting as a joke about Zoro and Hiyori sleeping together.
Cinera
However, considering that all the other Supernova in Wano damaged Zoro (Hawkins, Apoo) and for the purposes of hyping them up, I did think Killer KOed Zoro in part to legitimise him as a threat.
Cinera
That said I'm not sold on your conclusions. I did not come away with the impression that Killer was on Zoro's level. Killer would have never landed the hit if not for Gyukimaru's interference, while it seems Zoro would have eventually been able to take him down before receiving much damage (Killer was down by the first hit).
Cinera
As for the comparably nerfed hypothesis, all the Supernova Zoro has faced he engaged using only two swords. Yes Shusui was by far his strongest sword, and losing it was a noticeable drop, but if Zoro engaged Hawkins, Killer and Apoo with two swords, I don't think him having two sword vs Killer is to further a narrative of the two of them being comparably weakened.
Cinera
It's probably stupid to apply feats based powerscaling logic to an instance like this, but my conclusion after this was something along the lines of: "A full powered Killer is a level below Santoryu Zoro". Killer is stronger than the likes of Pica (the difference in their treatment is clear) but not as strong as Zoro.
That's the gist of it there. Oda does not go through with knocking Zoro out lightly. Sure, a part of it was to lead to the "Zoro and Hiyori slept together" joke, but it is still very unusual for Zoro to end up in that state after a fight. Which hypes Killer up to no end, which is ignored on this site