It isn't necessarily Oda though. It's WSJ that assigns editors. The likely reason why they keep changing his editors every few years and why they're often younger than him by at least 10 years or more (usually), is because it's a form of internship for these young up and coming editors. Working with Oda means there they get experience and fine-hone theirs skills and expertise under a great Mangaka with little to no risk of negative consequences which could arise from their mistakes. One Piece is just too successful and sells whoever the editorial team Oda works with. Never mind a few sales slumps here and there. It's been the flagship of WSJ for 20 years. That thing is as stable and permanent as Mt Fuji.
And I do agree Oda would benefit having a veteran editor or two who can offer constructive ideas while providing some streamlining and discipline to his overwhelming imagination and creativity, how many senior, successful authors have or would tolerate being told how and what to write as if they are newbie writers on a first time publication? I'm sure very few. Rowling, Jordan, King, Martin to name a few - once they're successful writers you can spot the moment they're no longer beholden to an editor and can basically write as much padding, rambling filler as they want.
Of course Oda's editorial team do get feedback, but why do you think they, or Oda himself would listen to fan suggestions, no matter how well intentioned, concerning how to write his own story? This isn't writing by committee. Oda writes what he wants, he's successful enough that he's like a demi-god as far as the industry is concerned, and the last thing he would ever want is to take fan ideas. He's even mentioned in interviews ( or maybe his editors did) and Greg has stated as such, Oda would change things up if he saw the fandom had predicted it. Even if it clashes with what he had established previously. The man is too proud ( and he has every right to be).
As far as the spoilers go...Kanjuro is a surprise. A competent antagonist who isn't even a Beast Pirate member.
Jinbei was not. The timing is interesting, looks like he wasn't to be the surprise element during the climax of Onigashima then.
The furore over how this reflects on BM though, is hilarious.