Yamato being introduced part-way through Onigashima gets worse the closer you look into her. Based on the scrapped concept art that’s been released, Yamato was originally supposed to show up in at least Act 2. But given how that same concept art also paints the creative process behind Yamato as Oda taking a grab-bag of ideas, loading them into a shotgun, and shatter-blasting the whole mess at a wall, it seems like the main reason Yamato went unmentioned for so long was because Oda had absolutely no clue what her main purpose or role in the story would be, or even what the focus of her arc should be, so he put off introducing or mentioning her as long as humanly possible to buy himself time to figure those parts out. Which, given the end results, doesn’t feel like he ever did.
What’s most baffling about Yamato is the amount of distance that has been placed between her and the Straw Hats. You maybe could argue that Yamato’s role in the raid was to serve as the stagehand/kuroko who takes care of all the behind-the-scenes tasks like the basement bombs, but that comes at the expense of her feeling weirdly disconnected from the overarching conflicts of the arc/climax because she doesn‘t build any connections to any if the major players outside of Momo so it has no benefit in that regard. Then even after the raid Oda continues to seemingly go out of his way to put distance between Yamato in the crew by skipping ahead several days at a time, and in most of those scenes she barely shows up or interacts with anybody, so her status with the main cast doesn‘t appear to have progressed at all from where she started despite being introduced over 70 chapters ago.
And it’s not like she would have nothing to add. She could’ve easily provided some unique insight during scene where the crew was talking about Pluton as Kaido’s kid given what Kaido said to her about Wano being special, but based on how this chapter plays out Yamato doesn’t appear to have any interest in being part of any of the planning sessions that directly effect the crew she supposedly wants to travel with.
If anything continuing to put off any it makes Yamato come across as though she isn‘t actually interested in building up a rapport with the other Straw Hats, or at worst that to her they’re simply a means to an end rather than friends. And trying to fit that in this late in the game means future arcs would be burdened with doing a bunch of character building that really has no excuse not being handled dozens of chapters ago.
[/ISPOILER
