I was a 4.
After the end of this arc though, it might've climbed to an 8.
Oda had the opportunity to create greatness with the finale of the Wano arc, but in the end, Luffy won because of a bullshit power that wasn't foreshadowed.
His enemy, whose defining belief and defining symbolism was the idea that strength ruled the world, got overcome by strength and subsequently died.
In the end, Oda blundered the story into proving Kaido right.
Alternative solutions would've been obvious. There were other fighters there.
We could've seen Big Mom betray Kaido in a moment of weakness, where he was doing something she considered particularly horrible, and weaken him because rule of strength makes for unreliable allies.
We could've seen a team up of Luffy, Kidd, Law, Yamato and maybe Marco to bring him down because alliances of ideology can allow for strength by overcoming differences.
We could've seen Momonosuke's adult form step up and demonstrate just enough Oden-like natural strength to be marginally helpful at a critical moment while gaining a nasty wound that his Zoan fruit allows him to heal. He could've proved himself a worthy next Shogun due to that.
We could've seen Onigashima's floating nature actually impact the plot in a meaningful way by having it fall on Kaido's head.
Oda is usually a masterclass writer in this stuff. His villains are always defeated ideologically as well as physically.
Buggy was defeated because Nami stole his body while it was in pieces, which happened because he insisted that stealing was a pirate's right and turnabout is fair play.
Kuro was defeated because, by targeting his own crew as well, Luffy was able to get used to his moves enough to finally catch hold of him, Luffy caring about people (particularly subordinates) lives while Kuro does not.
Don Krieg was defeated because, despite willing to go to any length to win, including getting up after Luffy was drowning unconscious, winning through such methods would've been pyrrhic anyway, and Gin wasn't willing to let him make that sort of mistake.
And Arlong was defeated in Nami's map room, which he didn't even realize was his largest hypocrisy of all. Even if fishmen were stronger and better in all of the ways he claimed, his dismissal and enslaving of humans due to his stated reason of poor capability was still unjustified since the entire crew of the Arlong Pirates were relying on Nami's maps anyway.
Wapol lost because he had already forsaken literally everything he had which made him a king: a status which he claimed put him in the right.
Crocodile lost because he didn't consider it a virtue to care about anything except for the mission. Thus, the interpersonal trust of Nico Robin, which was vital to the mission, was never gained, and he lost by fighting against someone whose
only purpose for being there was caring about a someone else, despite how it would literally never help him to achieve that status of Pirate King since they didn't even join his crew.
Enel lost because he couldn't dodge Luffy's final attack. Why? Because his Mantra didn't work that moment. Why? Because that attack wasn't aiming for him. Luffy was just trying to ring the bell. Why? Because Enel didn't understand the purpose and history of the bell. It was never something he looked into. Why? Because Enel was a man who actively scoffed uncaringly at knowledge, science, and historical context: The foundational trait to his character which allowed for him to call himself a "God" with a straight face. And the trait that brings him to the moon.
I could go on. These thematic conclusions didn't get any worse as One Piece continued. Until now.
I might take a break for half a year or something after wano ends (part of be still believes that there will be a miracle and Kaido will crawl out of hell for one final fight). At this point, I'm fully willing to believe that Oda has completely lost his touch when it comes to writing.