There are 0 reaons why Oda can't get help to make scripts, people to make sure everything is tied up nicely.
One Piece being long as it is, is more of a reason to get this kind of help. If Oda wants to write everything on his own, than his mistakes are his own. If he chose it, than so be it. And if he has this kind of help, and still come up with these trash ass confusing things, than it only makes the case worse.
But i'm not gonna accept whatever crap he throws at me just because "One Piece is too long and he is tired".
Same thing happened with those shitty ass Game of Thrones seasons after they didn't have any book to copy. It was a shit show since season 5. But people only opened their eyes after the abomination that was the last season.
All because the showrunner clowns decided "they wanted to have total control over the script" and didnt hire any help.