I'm for Carrot.
I don't think there's any point in looking at a work of fiction as a series of pegs to be knocked down or empty checkboxes to be marked, I think if the needs of the writer align a certain way, whatever way, then everything else can bend to make that fit. So I won't comment on those details.
But I WILL say, with my limited knowledge as a writer… with the way Carrot's been handled in the story so far, I don't see any way for her NOT to be on the crew eventually. If she leaves at the end of this arc, honestly I'll be completely baffled as to why she was ever there to begin with.
Once again, I don't want to comment on patterns or such, except for one thing. Her inclusion doesn't fit the pattern of other crewmates, but there's never been a pattern to begin with and I can't imagine Oda putting such a restriction on himself. But there IS a pattern to be noted, and it says a whole lot: so far, her role in the story has been wildly inconsistent with that of other characters who HAVEN'T joined the Straw Hats.
For the most part, Oda doesn't really let people be on the boat from one arc to the next without giving them a really good reason to be there. He wants the focus to be on the main cast, after all. The exception has always been for characters who enable the Straw Hats to go on the next adventure. Right from the moment she was named, Vivi was about getting to Alabasta. Law brought them to Dressrosa, Caesar was part of that arrangement, and the alliance is the throughline in the conflict against Kaido. Kinemon and Momonosuke kicked off Wano, etc. But Carrot? Carrot didn't get on the boat until they were already going to Whole Cake. Her being there had no impact on having them go to Wano. All that was already happening.
So what has Carrot DONE so far? If we quantify this in terms of plot points, her part in Whole Cake was twofold. She was motivated by Pedro's death, and introduced us to Sulong. However. The main takeaway from Pedro's death, though, was that it motivated Carrot, working as the turning point, if you will, in her character arc. And Sulong, meanwhile, will surely have greater plot significance later, but there were already Minks in that arc, and a whole lot of them in the arc before. There were other times to let us know about Sulong, but as it was applied in Whole Cake, the big impact of that scene was to hype up Carrot. In other words. Both of Carrot's plot points in that arc, were for the sake of developing Carrot. Oda's a busy man with a story to finish, he wouldn't go so far to develop a temporary teammate if the only development was going to circle around back to herself.
The real reason she was there, through Whole Cake and her small role in Wano, is to get us used to seeing her. The New World is super complicated, with a huge net of characters and plot points that overlap each other, so there's not really room to do a straight shot from Introduction to Join the Crew. So he's letting her endear herself to us, giving her small bits, and letting us see her as part of the group shots, so that we'll be already accustomed to having her be part of the team when it's time to leave Wano.
The only other characters I can possibly admit to being similar to Carrot in their role so far is Johnny and Yosaku, but... c'mon. They didn't have the emotional pull that Carrot did, they didn't bond to any of the main cast like Carrot did, and they were never framed in the team moments like Carrot consistently has been. Her big moment will come, either as part of a fight, as a dramatic farewell during the Big Party that Luffy mentioned, or as part of some unseen plot development. It couldn't be in the recent crop of chapters because, well, it's Jinbe's hour atm. But Oda was certain to show Carrot as part of that, and always framed as another part of the crew. Maybe I'm misreading this, but I don't see why Oda would go through that effort just to throw it in the trash when the arc ends.