Relationship development and character development are different things, Luffy develops relationships with characters in every arc, even enemies some times, but he himself very rarely changes (if at all)
Like I said her only development in Orange town was deciding to travel with Luffy, and even then she saw it more like taking advantage of the situation rather than becoming a pirate so its a shaky development
And I dont recall so many people being so against them like it seems to be with Yamato . I personally belive she will get more in the future since we lack all of her history prior to Oden, and Oda barely touched on her relationship with Kaido beyond their aniimosity towards each other and Kaido's own flashback was rushed as hell, so there is a lot that could happen
Yeah, ending in 2 chapters is pretty hard to excuse (if thats whats happening), I'll cling to a bit of hope that it wont suck since we are getting a buster call, or that he will just get to the party in these 2 chapters and that we will get a post Wano arc after the break, but these news suck
Yamato's connection to Ace who the crew met in Alabasta was brought also around half way through during the raid.
Yamato battled alongside Luffy and held off Kaido. She took care of the giant for Frank so he could focus on Sasaki.
Yamato also dealt with a situation to not worry Luffy while he was in the middle of a battle with Kaido when Momo was wanting to stop Luffy showing trust between Yamato and Luffy. Luffy trusts Yamato to stop Onigashima and Yamato trusted Luffy to beat Kaido.
Again your nitpicking scenarios to try justify why Yamato can't join when in fact she's done more than enough when you look at it objectively.
But… do you expect Yamato to get another arc focused around her? I don’t.
The significant difference between Yamato and Robin/Nami is that Yamatos villain was in the same arc where she joined. Robins wasn’t we never actually saw the world government until Ennies Lobby. Namis wasn’t we didn’t meet Arlong till later.
But Yamatos entire life was about Kaido and Oden. Two wano centric characters, I don’t know what could make her grow more after wano afterall
I don't expect another arc focused on Yamato no. I don't understand why it's so difficult to accept that Yamato's a pretty simple character (you can even call her static if you want), there's not much to develop regarding her.
She's a samurai fangirl that craves for adventue and freedom.