"I don't like the character so it must not have been made by Oda" - you can go look at Oda's literal notes to see that Yamato is his creation. I'll never understand the "blame the editor" mentality for parts of the manga that are not to the readers' tastes. I get that you're being sarcastic here, but it's become a pattern to blame editors / Oda's assistants for anything in the OP-verse that's not amazing, and credit Oda with the rest. Oda planned Wano for years (including Yamato), and I'd be very surprised if the assistants had much to do with the story beyond helping keep him
It is however only natural that readers who feel critical about something would also have a skeptical look on ever-changing editors, especially if those are the same age as the readers. I'm all for youth empowerment but ignoring maturity is also kind of disrespectful.
Part of certain quality lacks in Wano could indeed been very well due to editor changes. Wano must have been a tough product for anyone involved.
End of the day Oda never openly gives out much details about the production of One Piece, everything from his interviews, notes and the few actual photos of him or his workplace is carefully selected. The editors are too, and I since One Piece is the magazine's flag ship, I think certain higher ups from Jump and Shueisha are also informed and involved at all times. We can only speculate. Oda would be a lot more transparent about the production process in case we were not supposed to.
There are certain commercialized aspects about Wano arc such as the road to chapter 1000, or the little Uta cameo blob in Shanks recollection of memories about children. Shiki, who is much more unquestioned in canonicity was, end of the day, also most likely included to hype up Strong World back then...
If someone official would tell me "Yamato's early inclusion was for commercial reasons and the original plot was to have the character confined in a cave till the end of the arc, upon which it would have been revealed and taken in by the Straw Hats, with proper flesh out following in the next arc", I'd instantly buy it.
Because for a Straw Hat, the character is severely lacking. What is brilliant is that it is causing confusion to an audience obsessed with gender identity, that's a classical Oda, 10/10 he really knows how to play with his audience. As the usual "strong guy" Pell, Viper, Kyros kind of character, Yamato would easily work out fine, but for a Straw Hat? Any chance at a big moment is rushed over, with vs Green Bull we had this again just recently. There's also barely any interaction with the other Straw Hats.
The way One Piece is designed, it is a lot more flexible than you think it is, even tough it indeed has been planned through and through for years. Maybe next arc can sway me in, but right now I am just not feeling it. I think there are many that feel the same but are unwilling to admit, due to the character being a cause of controversy, and controversy does not go well in internet times.