The problem is that Oda is too slow. He likes to develop these side-characters like Senor Pink,Baby 5,Pound,Hyogoro,but the audience doesnt want that. I think that until Sabaody,the best One Piece formula was the one we all loved:
- The Strawhats arrive in a island,they meet some people,there is a villain to defeat,they defeat the villain saving the island
And this formula did work at the time,also because we always stayed in a island around a year,a year and a half,not too much.
Then,Sabaody happened,and i think Sabaody completely changed One Piece. Why? Because it introduced the Supernovas. These characters immediately conquered the audience's hearts,and the story changed to "the solitary road of the Strawhat crew toward the One Piece" to "The race for the throne. Who will win between the members of the Worst Generation?",and Oda knows that the story evolved in this way now,because in Dressrosa he made Doflamingo give his speech about it after he was captured,and also because he often talks in interviews how he didnt expect the Supernovas to be so liked by the fans. But,altough he knows that the story evolved in a different direction now,he kept following the same formula that worked before (Strawhats in a island,meet local people,save the island) and it also made it longer! (2,5 years in Dressrosa,3 and more years in Wano). But at this point i think this formula doenst work anymore like it used to,because the story evolved in a different direction.
Another element i want to talk about: Why,according to you,the arc Sabaody-Amazon Lily-Impel Down-Marineford is still so loved? Because it followed the new formula in which the story has evolved,without trying to conform to the old formula: there are not populations to save,there is just the full worldbuilding and Luffy going directly to his target,meeting important characters like Warlords and Revolutionaries (Boa,Jinbei,Ivankov,Crocodile). Imagine instead if Oda had tried to put the "old formula" into that arc: it would have been way longer! He probably would have made a long arc set in Amazon Lily,where Luffy,and maybe the rest of the crew,meet Boa and the other Amazonias,but Boa is not in power because there is some villain who conquered the island,so we get a Alabasta/Dressrosa style arc where the crew helps Boa defeat the villain and come back to power,and only in the end Luffy receive the news of Ace getting executed in Marineford in a few days,so he decides to go.
Instead,he decided to go directly to the point: Luffy conquers the Amazonians's trust in a short time,then he receive the Ace news. Imagine if all post-Sabaody One Piece was like that,going directly to the point. (And this doesnt exclude fights,because in the same way Luffy fought Marigold and Sandersonia in Amazon Lily,in other arcs Luffy and co. would have had their fights,just without all the island-saving parts). It would have been more coherent with how the story has evolved,in my opinion! Basically One Piece should have become like it is when we get the "chapters between the arcs" or the chapters of the Reverie arc...but without the off-screening of the most pivotal parts!
