I guess the subject is unavoidable, so I'll give my opinion which nobody cares.
Readers have very different ideas of how power level works in One Piece. For some people, the stronger character always wins and, more importantly, they always have an intimidating performance. This interpretation stems from moments in the past when top tiers showed absolute dominance (like Kizaru in Sabaody), although it must be said that those scenes happened for the best interest of the plot. Nevertheless, I'll agree that Oda will most likely make the stronger prevail in every duel (except if it's a Luffy fight). That said, it's not true that things are always so one sided, and there are many moments when things didn't happen like that.
Marineford is the biggest example. At the end of that battle, only two named characters died despite the fact that everybody fought against everybody. That means that the strongest couldn't really subjugate the weaker.
- We have people like Mihawk, who many consider to be close to Shanks' level because of their past duel and because of his title as the strongest swordsman, but this same Mihawk couldn't beat Vista, and didn't even look to be ahead. Mihawk also didn't defeat Crocodile when they clashed, and there are many panels of him fighting against other WB Commanders who didn't go down.
- Whitebeard was the strongest man in the world, but he never seemed to be ahead of the admirals in any of his individual confrontations (Kizaru was dodging and beaming him easily [chapters 570 and 571]). Of course, he was sick, but we don't know how much that really made a difference. Even though Whitebeard did get a moral victory over Akainu after Ace's death, he did so by attacking from behind, and even managed to lose half of his face despite the surprise attack.
- The Admirals couldn't really beat any of WB's top commanders and the only moment they got ahead was when Marco and Jozu got distracted. Part of the fandom underrate the admirals to this day because of that.
So the yonkou didn't beat the admirals who didn't beat the commanders. Oh sorry, Akainu killed Ace, but we know how and why that happened. Aokiji couldn't best Ace though.
Marineford is not the only occasion. There are many characters who were hard to beat despite their power level. Fox, Perona, Sugar, Jora, Law, Moria, the priests from Skypiea, and so forth. And it also happened that allies could stall stronger antagonists too.
The main thing is that there are a lot of tactics in One Piece. Fights tend to play out considering the type of ability people have, not to mention little moments when minor characters do something useful, like when Mr. 3 stopped Magellan, or when Crocodile stalled Akainu, or the Strawhats doing shenanigans throughout the series. Besides tactics, circunstance also plays a role. While Jimbe and Robin performed a surprise combo on Big Mom, Queen alone bit both Luffy and Zoro and spat them on the floor, lol.
It's pretty clear to me that the weaker can hold a fight against a stronger opponent. What's weird to me is the opposite, actually. I was personally disappointed when Kaido one shotted Luffy in their first encounter, which felt contrived for the sake of raising the stakes and making it more awesome.
Fights in One Piece can happen in many different ways even if the strongest will win at the end. What matters is to see how it happens and evaluate by the coreography.
Kaido vs the Scabbards definitely doesn't betray my interpretation how fights happen in One Piece. The scabbards are nine really strong people who were shown to be on par with the Yonkou Commanders, and sometimes even above them (Sulong cat and dog)… and right now they are having the fight of their lives, and performing a lot of tactical stuff. That's a big deal! And despite all that Kaido will win, damn! Can you even imagine Luffy holding up against all nine of them? lol
One thing that should always be remembered, like it or not, is that fights in One Piece are always driven by plot. Oda is not playing a D&D campaign and throwing dices according to the characters' stats. For some readers this might be the superior form of storytelling, but that's not the author's intention for this series. Oda draws his fights for the sake of spectacle and drama and emotion and to accomplish the narrative beats of his stories.
That doesn't mean that he'll blatantly ignore power levels, or that everything is plot armor and asspull, but Oda will squeeze and stretch the fight in all direction if it's cooler or more dramatic or more spectacular. As I said before, you have to evaluate it according to the coreography, if it's convincing or cool enough for you.
Even when the main characters can't defeat the villains, it's always for the sake of plot and the consequences are proposital. Aokiji scared them, but didn't kill anyone. The Strawhats needed to be defeated in Sabaody. Ace needed to die. It's all according to plan.
Personally, I like this way better.
I decided to write this topic because the Yonkou are the biggest targets of controversy. The thing is: it's true that the story hyped the Yonkou, but I think that many fans hyped themselves a hundred times more than what was asked for, honestly.
They were presented as the strongest pirates alive, an elite of characters who are the strongest in the world alongside a few others. However, for some fans it's not enough for them to be stronger than other great pirates, or to be twice stronger, of thrice stronger, or five times stronger, which is more than enough. In the eyes of these fans, the Yonkou have to be 1000x stronger than anything else and be god-like creatures on Earth who shouldn't be touched.
I don't know how people got there, or how Kaido and Big Mom could be seen as below the concept of Yonkou. I look at them and I see the power, the crew and the territory, and how far above every other pirate they are. They take blows, but they bounce back.
What many argue is that the biggest problem is that, besides being Yonkou, Kaido and Big Mom are villains, therefore their lack of efficiency kills the tension and makes for badwriting. Their premise is that villains should be unfallible until the last fight, otherwise it's boring and disappointing.
Well, this might be your personal criteria, so bad luck for you, I guess, but this is not a writing rule which dictates good and bad writing. Making unfallible villains is common practice because it works (meaning: people like it and get invested), and it's an easy thing to write. The drawback is that it can become dull or too obvious or cliche. One Piece has done this before with success, though. Crocodile, Enel and Doflamingo were semi-unfallible villains who are adored by the fanbase. Crocodile is a personal favorite of mine.
However, what's funny to me when I see this argument is that tension in One Piece never worked with me ever since the beginning of the series when I realised that the good guys would never fail (Ace and Sabaody were the exception, but for plot reasons). I don't really get all nervous and impressed when the villains are portrayed as invicible monsters since I see through the facade, so it's not like I'm losing anything when Big Mom and Kaido started to take some hits that have minimal consequences to their physical integrity. But this is only my subjectivity, so good for you who can get all hyped up with villains in OP who look unbeatable.
It would be better for me if I felt tension in OP, of course, but that's not all there is to me. In case you're wondering, the lack of tension doesn't kill my vibe as long as Oda delivers in other aspects, like a great visual depiction of the fight, or creativity for the composition of the means by which the heroes overcome their enemies, or the showcase of emotion in the battle, or how the fight beautifully interweaves with the drama outside of it.
And there's another thing that I disagree, which is that Big Mom and Kaido taking blows make them look terrible. Once again, this is subjective, so I accept your feelings, but I simply don't see it like that. But I'm minority here, since that's how our anime community rolls nowadays, especially seeing how people love to spam Ws and Ls all the time. You can even see it affecting the Strawhats and how much they are valued by the community each arc according to their Ws and Ls.
What's interesting is that Oda could easily have written Big Mom and Kaido very differently, because it's merely a matter of choice. It's interesting how deliberately he chooses to make the Yonkou suffer all these blows before bouncing back again. Funny.
Are the stakes gone now?
Well, I don't think so. Unlike most people, I do see Kaido as a really impressive villain in terms of power, especially because he'll defeat all the Scabbards. You see, if Kaido just wipes the floor with them easily, it doesn't look like a feat, because the samurai will look like unmemorable ants in a forgettable fight. However, if they look impressive and powerful, then beating them start to look as a real demonstration of power during an iconic battle. Good stuff!
Obviously, my impression of Kaido is largely based on how I imagine that things will play out next, and I believe Kaido will turn the tables defeat the scabbards in beautiful fashion. To me, he's just like a raid boss from a mmorpg, which is quite amazing.
Funnily enough, despite all the flak he is receiving from the fandom, at the end of Wano I think Kaido will be a villain very similar to Freeza from Dragon Ball, who is one the most iconic villains in shonen history. For those who don't recall, Freeza was introduced as the strongest being in the universe with a staggering ki of 513 thousand, which was many times above anyone else… and then he could double his power level any time he transformed, and he could transform 3 times, and then keep raising his ki in his final form. But despite such a huge power creep, we kept seeing Piccolo, Gohan and Vegeta managing to hurt him and forcing Freeza to unleash his next form until the very last one, which could only be matched by Ssj Goku.
That's what I imagine will happen with Kaido. He'll just keep evolving as he shows his next form as the heroes keep surpassing his expactations. Dragon form, human form, hybrid form, awakening, who knows what else… just insane!
So what I can tell you guys is to wait to see the full picture. Cheers!