Wano was pretty much the Litmus test to see how Oda would handle the final arc, and I am really worried now. Similarly, Captain America Civil War was the test to see if the Russo Brothers could handle Avengers Infinity War, and Endgame. That movie was really good because it managed to handle a large cast of characters, while never losing sight of its plot. It had to give a valid excuse on why Stark would go out of retirement, and set up everyone's motivation to pick a side. It had to be a Captain America sequel while also being Avengers 2.5. It had to introduce Spider-man, and Black Panther into the story. In the hands of other directors, and studios it could have been an absolute disaster, and they handled it like champs. This was possibly RDJ's best performance in the MCU. I remember going out of the theater with my bff extremely excited for IW, and that movie lived up to the hype. I did not love Endgame but it was still a worthy finale.
Wano still had its moments but Oda messed on parts where he should have not that you pointed out. Civil War challenged our heroes in every way while Wano did not. I had this whole scenario that Blackbeard would come, make the raid fail and declare himself as the son of Xebec, and revive the Rocks Pirates thus becoming the greatest threat the world has ever seen (teased by Garp). My act 4 would have been about the crew raising from the ashes with Zoro surpassing Oden and rallying the people of Wano to take matters into their own hands. I had this whole image that CP0 would give into Orochi's demand to bring Vegapunk to his country as a way to bring Smoker, and Tashigi into the story. This time the marine duo would protect the Straw Hats. In my headcanon, Tashigi was gonna teach the weaker Straw Hats Haki, and a heart to heart moment with Marimo. Sandai Kitestsu would have been destroyed in the raid thus giving Nidai an actual role. Momo would have entrusted Ame No Habakiri to Tashigi. I would have explored how Zoro's past in Wano, and how he landed in East Blue. I would have started the epic tale of Luffy, and Smoker teaming up and taking down the Rocks pirates like Roger, and Garp before them.