I think that Oda’s issue is his creativity. It’s like he has too many ideas and while they are creative, not every idea is going to fit into an arc or story. If I was Oda’s editors I would say your arc gets 50 chapters at most. Part I: The set up Part II: The Climax and Part III: The Resolution. He can divide the chapters however he wants. I would be adamant that he start answering mysteries and revealing lore that readers have been waiting for.