There's never a case in which a straw hat is introduced so late into an arc and then joined at the end of that arc. And this isn't just some random pattern either. It's done so that readers have the biggest impression of those characters since they are some of the first things seen of the new island. In addition to allowing for way more time for development of the character throughout the arc.
Let's provide some proof:
Romance Dawn - Chapters 1-7
Zoro - Name dropped chapter 2, Introduced chapter 3
Orange Town - Chapters 8-21
Nami - First appearance chapter 1 colour spread, Introduced chapter 8
Syrup Village - Chapters 23-41
Usopp - Introduced chapter 23
Baratie - Chapters 42-68
Sanji - Introduced chapter 43
Drum Kingdom - Chapters 130-154
Chopper - Introduced chapter 134
Alabasta - Chapters 155-217
Robin - Introduced chapter 114, multiple arcs in advance
Water 7 - Chapters 322-374
Franky - Name dropped chapter 327, Half intro chapter 329, Full intro chapter 335
Thriller Bark - Chapters 442-489
Brook - Introduced Chapter 442
WCI - Chapters 825-902
Jinbe - Name dropped chapter 69, Introduced chapter 528, waaaay in advance
In some cases, straw hats are introduced way before the arc they join. But they are
NEVER introduced late into the arc. And as mentioned above, there's specific reasons that's the case. Just look at the scabbards. 5 of them were introduced before Wano even began. Kiku was introduced extremely early in the arc and then the Kawamatsu, Denjiro and Ashura Doji were all foreshadowed early on and were then teased even further with Holdem mentioning AD before his intro, Kawamatsu's constant silhouettes and Denjiro being Kyoshiro all along.
Things would be a bit better if Yamato was supposed to be some secret child that people didn't know about. It would explain why there wasn't a single mention of her for 70 chapters. But that's not the case. Everyone knows about Yamato, including BP fodders, Ulti talks about Kaido's family issues as if it is a regular occurrence, yet there were no name drops, mysterious appearances or anything regarding Yamato. Yamato only being mentioned a measly 4 chapters before appearing, despite the arc being 70 chapters long already. Pudding, a character in the exact same situation as Yamato as a daughter of a yonko was shown waaaay in advance all the way back at Fishman Island with intriguing ellipses and an apparent disgust towards Big Mom.
Ain't none of that for Yamato.
Compare that to Carrot...Zou arc started chapter 802, they arrived on Zou in chapter 804, which was also the same chapter Carrot was introduced in.
The last straw hat has to the toughest job of trying to feel like a real member of the crew that has shared in their experiences, despite joining the latest. We're so far into the game and they've missed so much already that it would only make sense for Oda to try and include them in as much of the journey as possible. A character joining the crew that was introduced in Wano was already tough enough since so much has happened, but for that character to be introduced this late into the arc, also with practically zero foreshadowing and build up is simply taking the mic. Carrot's been with the crew since Zou and has fought an emperor with them and saved their lives fighting a fleet singlehandedly for them. It's clear which character Oda's been working on for a long time in building relationships both with the crew and with the readers. And it's not the one first introduced 75 chapters into the damn arc.