See, I don't mind this in theory, but if this were the case, why would Oda have chosen to sideline her so terribly during the arc, to the point where she couldn't even get revenge on Perospero herself? This has always been my main issue with the Carrot 4 Nakama theory. Oda isn't even hiding how little he cares about her.
And if she "isn't strong enough" to defeat Perospero, he could at least have dedicated more panel time to the fight instead of off-screening it, to show that we're meant to care a lot about this encounter. When even the mangaka doesn't seem to care, why would the reader care about her? He didn't even give her a small sidequest to show her usefulness, like you would do if you wanted to set up her joining.
I've also seen people say, "well, Oda sidelined her in Wano because her time to shine was WCI", but really? There's sidelining, and then there's giving her like the #60 spot in total panel time for the arc.
Idk, Carrot has been handled in a very bizarre way.