Quite the opposite. The same argument supports one and puts down the other.
Carrot's been in the story, travelling with the straw hats on their ship as a close companion from Zou, to WCI and now to Wano where she is playing a role comparable to a straw hat. Carrot had no reason to go to Zou, yet Oda brought her anyway, and then gave her one of the highest panel counts out of everyone in the arc, beating multiple straw hats. Despite, yet again, having absolutely no in story reason for her presence in the arc. She was the first character introduced after the straw hats arrived on the back of Zou and has been with them ever since. Oda's clearly developing her and didn't just randomly decide to bring a character along for the funnies.
Yamato on the other hand was introduced very late into the final arc of the saga and the culmination of almost a decade of work. Given only a handful of chapters of buildup, as opposed to other significant characters in the saga like Pudding, Jack, Orochi, Oden who had been hinted at hundreds of chapters in advance.
Chiffon was also the daughter of a yonko that she was going to betray, she'd also been abused by said yonko, she was the wife of a supernova and had ties to old friends of the crew. Not to mention knowledge on Big Mom's past You could say she was significant if you want but...
Fact of the matter is, we're reaching the culmination of an epic saga and this character has just been introduced at the very end of it, with hardly any build up leading up to it. As I said before, there's a reason Franky wasn't introduced just before the battles for the keys.