The main difficulty of writing a serialized story is you don't get to change your story often. Authors usually rewrite stuff dozens of times before it's released.
That doesn't seem to have stopped Oda though. He not only changes large plot schemes, but even little details are inconsistent.
In the chapter where Sukiyaki is telling Law and Robin about Wano, he first says he doesn't know how Ancient Wano became this way, then he immediately goes on to explain exactly how it happened. There's just zero attempt to be consistent.
I also love how people act that Oda wasn't this bad pre timeskip. He was, just not on this scale.
For example, I will give you Alabasta and Wano finale.
Luffy gets beat up a few times, uses a ridiculous power-up, and wins in the end.
Reminds you of something? Hell, yeah! Kaido vs Luffy is basically Crocodile vs Luffy but on steroids obviously.
Zoro and Sanji power-ups in Enies Lobby.
Zoro pulls up some fucking Demonology and Sanji lits his leg on fire.
They just fucking do it, they don't explain why or how they came up with it, especially after Water 7 flop vs CP9.
Same goes for Luffy's Gear 2.
Luffy is basically like: "Sooooooo I just came up with this Gear 2 thing".
How? When? Why?
Lmao. I hope more people understand that Oda was never the man people remembered him for, mostly people who praise him for pre timeskip do it because they were kids and didn't know what good writing is.