A lot of people have mentioned that Oda did a fantastic job at crafting an immersive and believable fantasy environment in the form of his One Piece world, but Oda's crafting of his world isn't that good tbh, considering there's so many aspects surrounding it in the narrative which just make no god damn sense.
He sprinkles in tidbits of world building to expand his world and its cultures, but at almost every turn it ends up adding more questions and exposing how shallow this world really is.
It's bad world building, since so many of its facets don't have the proper growth or evolution to make them feel like realistic societies, even within his own fictional world.
There's a huge distinction between a plot element being central to the STORY compared to being central to the WORLD. In a lot of stories, the world is built in a way where important plot elements, whether they be locations, objects, or people, that are extremely pivotal to the story being told, aren't treated with undeserved importance in the larger scope of the world. A good author should be able to properly distinguish between the two, and world build accordingly.
Leaving things ambiguous is one of the best ways to make your world feel larger. The issue is that he goes out of his way to add things which make no sense and end up making his world feel even smaller.
This is one of the many examples that just ends up making the world feel so much smaller than it should. It's like the world was completely stagnant and frozen until Luffy was born, and all the people in this world not connected to him might as well have never existed.
Oda has a magical ability of somehow managing to only add details to his story which harm his world building, rather than adding details which could enhance it.
He is outstanding at world generating. For a weekly series, there’s nothing else that even comes close to it considering the time-restrictions he has.
But he is average at world building. Putting it all together. The world feels empty and non-existent without Luffy and the straw hats present.