It's amusing how it's now basically an almost political confrontation between "Carrot supporters" and "Yamato supporters" as if there's an election for next strawhat and the choice is among two equally relevant but antithetcal candidates.
I can't really fault anyone for liking Carrot or wanting her to join… but i'm really surprised that some are so adamant in saying she will join, bacause right now i really don't see an actual reason to inform such confidence, except maybe the chance at a "see, i told you so" down the line. She's been around for a long, long time... and yet had nothing really about her. Saying that new strwhats till now all had strong motives or were relevant when they appeared is only half the story- they have motive and relevance that tie in into the arc plot and progression of the arc at hand.
Even in her high days of relevance Carrot was… just there. She helped, she reacted, she made friends, but nothhing since zou would have gone down a different path without her.
Yamato, on the ther hand, with a fifth of Carrot's total screentime at disposal brought his conflict with his father at the center of the arc, bonded with Luffy over it, was literally freed of his physical bonds by him and by him enabled to sort out his mental ones, which he's doing right now, and put himself in a situation where he now needs an actual, stated good reason not to join at the end of the arc, while carrot is still waiting for an actual, stated good reason for joining at all.
Not to mention the biggest question: "then what?"
This may be entirely a problem of lack of imagination on my part, but i really don't see how carrot could be extensively used as main cast going forward. she's basically a nami and chopper fusion, to me it looks like she'd just overlap with them in gags and side commentary.
Yamato, like him or not, has an immense charachter potential, and even if his charachter turns out underwelming… he remains a huge powerhouse addition going into the endgame, while on the other hand you have someone who was written as capable of putting up a decent fight once a month, provided it's not cloudy. That's actually pretty diifficult to factor consistently into a action battle story.
Again, there's nothing wrong in saying like "i wish Carrot would join cause she's fun to have around and i like her charachter" and so on, but after seeing how she's been written into the story… it's really hard to see where the "i'm pretty convinced carrot's main cast material" are coming from.