Oda is just continuing the Oden reflections onto Yamato. It was apparent from Yamato's introduction that Oda has deeply intertwined Yamato's story with that of Oden's. Proceeding to focus on Yamato in a Oden-like fashion is exactly what should be expected. I have said this several times before, Yamato is the one character in the series that benefits from not having character interactions with each of the Straw Hat Pirates prior to their inevitable likely inclusion within the Straw Hat Pirates. It is such an Oden thing to do and for a character that has been has been closely aligned with Oden, it harmonizes so fittingly. Yamato has been intentionally set-up this way and Oda has been intentionally avoiding Yamato meet the rest of the Straw Hat Pirates in a purposeful way beyond Luffy.
The relevance of Oden cannot be overstated. The way Oden has been focused on within this arc constructs his presence to be meaningful long after the Wano Kuni Arc ends. Oden has become the benchmark within this arc. Every single major player within the arc has been compared to Oden and his capabilities. Luffy through his Oden-like personality of being free. The Akazaya Samurai through the positions they hold and their inheritance of Oden’s will. Kaido through his desire for a challenge and his feelings of loss to Oden twenty years ago (which is part of the reason he is so frustrated with Yamato). Momonosuke through his journey to become a man greater than his father which includes his current form that likely resembles Oden from twenty years ago. Hiyori through the conviction and resolve she effects sourced from her father being such a great Samurai. Zoro through the path of becoming the World’s Greatest Swordman which involves him having to wield Enma as easily as Oden. And Yamato, who has embraced the spirit of Oden as a source of inspiration and strength consequently styling himself and behaving in an Oden-like manner. You could even argue that Orochi wanted to be like Oden as illustrated by his desire to match Oden’s legendary hour long execution by bathing himself in boiling water.
Oden and what he represents has become a concept relevant to these major players within this arc and will continue to hold relevance beyond it. To the world outside and the current World Government, the most famous Samurai isn't Ryuma but it is Oden. The only Samurai to have completely sailed the Grand Line was Oden. He was part of the Pirates King's crew. And without Oden, Roger would not have been able to usher in the Great Pirate Era. Oden's very presence and actions helped create the waves that continue to resonant across the seas within the One Piece world. Oden may have died but his spirit still lives on. Yamato will carry on Oden's will and remind the world (and the World Government) that Oden's spirit still exist. I believe that without Yamato, Luffy will not be able to fully embrace his destiny of fulfilling what Joy Boy left incomplete. In the same way Roger wouldn't have been able to completely sail the Grand Line without Oden, Luffy won't be able to finish what Joy Boy started without Yamato's help. And in the same manner Oden learned about the Kozuki history through his journey, Yamato will learn about his family's history through his journey (Elbaf and Vegapunk Arcs).
The way Oda has set-up Yamato's character is so incredibly fascinating. Even when Yamato has not been in focus, his story has been moving forward. It can be argued that Yamato's flashbacks weren't that significant but in the same breath, it can also be argued that Oden's flashback was also one related to Yamato. Without knowing who Oden was first, the reader's wouldn't know who Yamato is. Along with Oden's flashback's relating to Wano and Oden, it also serves as Yamato's backstory that helps explain why he is currently doing what he does and why he behaves in the way he does. Oden's flashback helps establish who Yamato is and what he plans to do going forward.
Yamato may not have physically met all the Straw Hat Pirates but the shadows of his presence has been set-up by Oda:
- When Franky finds out who Yamato is, he will realise that Yamato is a friend (protecting Momonosuke and taking out Haccha in one hit)
- When Sanji finds out who Yamato is, he will realise Yamato is a friend (protecting Momonosuke)
- When Jinbe finds out who Yamato is, he will realise Yamato is a friend (holding off Kaido single-handedly while Luffy recovers)
- When Zoro finds out who Yamato and the relation he has with him (Yamato has inherited Ushimaru's will), he will realise Yamato is a friend
- When Robin and Brook find out who Yamato is, they will realise Yamato is a friend (assisted them through Fuga during their fall when evading the CP-0 and not getting burned by Kanjuro's Kazenbo)
- When Usopp realises who Yamato is, he will realise Yamato is a friend (stopping Kanjuro's Kazenbo that Kin'emon will tell Usopp about)
Since Brook and Robin realise the Road Poneglyphs still needs to be located, they too will head toward the basement which may entail Yamato indirectly assisting them through his actions.
Going forward Nami and Chopper may even note references to Yamato from other characters. If Nami is set to assist Momonosuke by producing clouds, she could learn about Yamato from him.
Interestingly though, Oda has already included a development that has Yamato's actions already indirectly assisting the Straw Hat Pirates - the Vivre Card Yamato gave Ace which in turn Ace gave to Luffy. Thanks to that action, Nami came to find out about the existence of Vivre Cards and since that moment questions and wonder surrounding its application and mechanics began to run through her mind which is why when she met Lola and received Big Mom's Vivre Card, Nami was able to ask the right questions and find out more about Vivre Cards. This in turn led to Nami having the knowledge she could leverage to take advantage of Big Mom's Vivre Card when she adventured across Whole Cake Island (since Nami still has part of Big Mom's Vivre Card, this will come into relevance in a future arc). The Straw Hat crew and fleet are connected by Vivre Cards and for someone who knows how to make them to join the crew, it just seems right. Nami will recognise the value Yamato has when she learns of this skill and the information Yamato possesses.
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Yamato has also been following the Straw Hat Pirates since the Battle of Marineford. Through each article Yamato came across of the Straw Hat Pirates, there is a story of how he reacted. How he prepared himself for their inevitable arrival on Wano Kuni. And lets not forget that Yamato has his own 3D2Y moment. Yamato considered Ace a dear friend, one of the few he had, so when he saw the Vivre Card vanish, grief, anguish and despair washed over him. But it was in that moment that his path forward revealed itself. Only AFTER Ace was killed did Yamato realise the importance of Luffy and how Luffy related to the journey of Oden and Roger. Since that moment, joining the Straw Hat Pirates and assisting Luffy has become one of his goals (along with freedom).
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Oda's writing pretty much expresses itself as Oda fashioning Yamato to be a Straw Hat Pirate. The potential is there. Existing. And continually moving forward with more and more momentum.