I'd like to add some thoughts on the "lack of tension"/"lack of climactic setback" this arc has. This is all my opinion, of course, but it may help explain why so many people feel the stakes were kept low.
1. There was no point in the battle we felt the heroes were really danger
Around the chapters that would form Volume 100, I was constantly getting the feeling that "now we are about to endure the darkest phase of the fight", but the following chapters would always defuse the situation, never allowing things to escalate out of control.
For instance, Luffy fell off Onigashima and Kaido is loose on the island. Now THAT seemed like a huge climax in which hopes should faulter. And yet, we see Luffy rescued and Kaido kept busy by Yamato soon after.
I'm too busy and lazy right now to re-read the entire Act 3 right now and find all the instances of that, but there were several.
2. The villain moments were often off-screened
Another factor that I feel helped keep the stakes low was the amount of off-screening we got, and that it affected mostly the villains, Most often, when we cut to a battle, the villain is in advantage, and we never see how the situation got to that point. We usually get to see the heroes standing back and gaining the advantage, but that downplays the villain's threat and makes the struggle seem not that hard.
Examples of that happening: Kanjuro vs Kiku; Ulti & Page One vs Nami & Usopp; Big Mom vs Kid & Law (twice); Perospero vs Nekomamushi; Jack vs Inuarashi. We are told how dangerous those guys are, but never actually shown, because when their battles get panels, it's for the heroes' comeback/escape.
3. Lack of consequences
Marineford War was a big deal because people died. When Luffy passed out, we were truly frightened for him, despite knowing he would survive. We felt there would be bad consequences, even if he survived.
I feel that all the Scabbards not only surviving, but also getting up to fight again, really defused the tension in the entire war. When we got to the rooftop in Chapter 1,000, I remember people expecting to see the scabbards out, maybe some of them would be dead. Nope, we get confirmation they are alive (via Kin'emon) and Law teleports them to safety. Oh, but they are out of the fight, right? We even get scenes later that show they are endangered and need saving?
Nope, let's make them all get up after being bandaged by a mysterious helper. All are able to fight again.
That put in our brains the certainty that the heroes will survive and win. That even the World's Strongest Creature is not that big of a threat.
4. Luffy "feeling like Goku"
In all arc-ending fights, Luffy has always struggled. We see the anger and desperation in his face as he must defeat this enemy or all is lost.
It was really strange to see Luffy smiling as he fought Kaido. It took all the desperation off the situation. Luffy was no longer fighting an unsurmountable opponent, but an equally strong fight. And it happened twice: once he learned the secret to Advanced Conqueror haki, and then again as he got back to Onigashima. Between those, there was the major humbling experience that was Luffy getting knocked out (off-screen, so we missed Kaido overpowering him…), so the second time Luffy shouldn't be smiling, IMO.
I get it that Luffy is smiling because he feels he's at an Emperor's level finally, so he's close to his dream of becoming the Pirate King. But this is a war, people are (should be) dying. There should be more stakes than Luffy proving himself. If Luffy himself is so confident and secure, how are we readers meant to be fearing for him?
Oda has more than proved he's an amazing writer, but I see Wano Act 3 and I feel like he went to such a gigantic conclusion for this Emperor Saga that he mishandled a few things.
I feel he should have gotten some players off the stage earlier, so that the remaining characters get more screentime. I feel at least one Scabbard should have died early (probably Kiku), and some of them should not be able to get back on their feet (what have Kawamatsu or Denjiro done so far since they got back up?). I also feel there should have been only one Jack fight (the earlier one on the roof, against Inu and Neko), as the second one was really uneeded (IMO). I feel the entire presence of Perospero felt weird and could be supressed, as it meant to close up Pedro's story, but felt tackled on. I feel Luffy's fate after losing on the roof should be kept hidden longer.
One Piece is never bad. But I do feel Onigashima has some pacing and tension issues that need to be pointed out.
Great read. I 100% agree with you.