I would like to talk about the greatness behind the construction of the latest chapter.
The Scabbards are not just the Side Characters.
Denjiro, Ashura Douji, Kawamatsu were touted to be as three strongest Samurais in Wano, the same Samurais due to which even Akainu was hesitating to send his forces in Wano.
Wano is regarded as a strong country due to the same Samurais. Inuarashi and Nekomamushi fought with Jack on equal terms who is a freaking Yonko Commander. In short at least 5 of the 9 Red Scabbards are either Commander level or near. Izo was a Whitebeard Division Commander, Kinemon was like the first mate of Oden and his skills are no joke, Kikunojo and Raizo are somewhat comparable to the Flying Six.
Furthermore, all the 9 Red Scabbards have Ryou and mind you, Ryou is the technique which is hinted by Oda as the only technique which can pierce Kaido’s skin and also it was hinted in this chapter that Kaido was saying they had Oden’s Ryou specifically, let’s wait for further explanation.
Willpower is one of the main aspects of the One Piece and it has been consistent throughout the series, in fact, Haki is a byproduct of willpower.
In dire/desperate situations willpower blooms even more. The Scabbards had to suffer for 20 Years, Ashura Doji lost his entire crew who tried to raid Onigashima, Denjiro had to work under a scumbag and was engulfed in extreme rage, Kawamastu had to suffer for so long in Udon, Minks suffered a lot in Zou due to Jack and for Kinemon & co the wounds were fresh as it was just a few days ago when Oden sacrificed for them. They all deserved a shot at Kaido.
Yonkos are not Gods and Mental State
In One Piece villains are not flawless beings, they are not your typical overpowered “you can’t touch me beings “, they have flaws and quirks that’s what makes One Piece unique from its contemporaries. It would have been so easy for Oda to make Kaido like Madara and one-shot everybody and later a team-up of Supernovas and Scabbards taking him out but nope that storytelling is cliche, this is not how Oda writes his story.
Kaido’s biggest flaw is his drinking habit and mental state. Even Luffy was managed to hit him in his drunk state but later when he sobered up he one-shotted him.
Same way here as soon as Kaido sobered up he was serious and turned into a dragon and is now ready to wipe them up on the rooftop.