Sorry this is not solid ground evidence at all.
Just your subjective opinion on the character designs being similar which I subjectively disagree with.
Not even one of Chopper's forms is similar to Carrot. I would love to rule out Carrot visually but it just isn't happening. The only similarity you reach for is fur and animal inspired.
I don't think that's enough to stop her from being included. Sulong = Werewolf, its quite different from the Human Zoan awakened drug induced transformations Chopper does.
The character designs are very different in race, size, shape, gender, role, silhouette, height etc. They both also assist each other as characters with the Bropper dynamic as seen from their interactions. My job is character/concept design so It's just my opinion but it is also informed from experience. I don't think Carrot and Chopper's designs cancel each other out otherwise she wouldn't have even left Zou. If anything Minks seem to be quite important and there is no mink in the crew.
Trust me I don't want another furry character on the crew, but I still don't agree with your point at all even though I want to dismiss Carrot as a member.
Shachi and Penguin are almost carbon copies, that doesn't stop them from being central characters on a crew too. Too big of a stretch for me.
Also as all the other people in the forum posted it's obvious you are just hating the furry meme. I understand disliking it but it's clouding any logic you have for reasons she might actually be in.
You're whole reply is mistaken, I'm not talking about designs. but about concept.
Samurais, other fishmen, cooks, musicians, robots, furries. all covered.