After that concept art I feel Yamato's chances of joining dropped significantly. The many different concepts, one of which is seemingly incompatible with the Ace connection (not sure about that Kozuki hating Yamato concept's timeline, might have misinterpreted), doesn't make it seem like Yamato's long-term story role or existence was planned much until Wano.
The biggest problem imo is the 3 eyed tribe concept. I really doubt a character who was considered to be made one was ever a serious potential Straw Hat when Robin exists.
Dumb shit here, there only one real concept thats different most of the others is Yamato changing fighting styles from kung fuu/Martial Artist and swords to using the Kanabo like an Oni.
Nothing there contradicts Ace.
All strawhats have had different concepts.
Nami was originally an axe weilding Cyborg woman, then a Spear welder that had nothing to do with Navigation before we go to the version we know.
Sanji was originally a gun slinging Cowboy who wasn't a cook, before Oda took the character into a different direction.
Usopp was supposed to be the Vice Captain
Zoro was originally supposed to be Buggys right hand man and a brother to the Pirate Clown before joining.
Chopper was not the lovable mascot character but a chain smoking swordsmen
Robin was a man who loved plants not history.
Ever character has changes, every story, character theme starts out as a concept and is worked on and such.
Shit Kumas a way different character then how he originally was, hell his original design is pretty much proto Shiki
Ever go see what the early concepts for Naruto were they were awful.
Go look a Zabuza and his pet Bear companion Haku, Sasuke and Sakura for better or for worse were never originally intended to be there which changes alot of Naruto without them, Animal People as hokage and teachers.
Did you know Resident Evil 2 Remake was originally concept and developed for a while to keep the fix camera perspective of the Original and keep it in line with Resident Evil 1 Remake