No, I'm saying Yamato wasn't intended to join but Oda made it look like it for business purposes. No need to continue debating anything (it will happen anyways), if what I'm saying is correct (it could be not, of course) then his job is already done as Yamato is very popular and is fueling both engagement from customers and merchandising sales.
Oda isn't deciding MAIN CHARACTERS, Oda is taking advantage of the readers wanting crewmates in order to bait.
Indeed, you can't expect an old man with an idiotic method of working supported by one of the most poisonous cultures in the world to keep delivering a good product after it has become a business empire.
I'm not defending anybody, just commenting on the obvious reality that Oda is an employee of businessmen who want to make profit of the product they (not Oda) own. And if they can make profit out of the nakama expectation, then it will happen. And again, I may be pessimistic here and this wasn't what truly happened, or who knows, Yamato may join in the close future, but I just don't trust art turning into a monetary empire.