1st.
Luffy DOESN'T EVEN KNOW IF THE ONE PIECE IS REAL OR NOT, teeling him about its existece is a huge spoiler for him. More spoiler if he talks about how Roger reacted, wich is a huge spoiler for Luffy.
2nd.
Yamato fighting Kaido now doesn't mean a shit when we saw Yamato fighting against Ace (Who wanted to freed the citizens) Yamato was against that Wano Citizens 2 years ago, now he defends them because he want's to sail out, he doesn't give a fick about them to be considered Deity (FOR THE MOMENT)
Yamato can easily see how bad has left Kaido the country, and try to help the citizens... Being a new Oden and a Deity...
4th.
Every Mugi has been presented doing some stuff related to their rol, maybe Robin was the exception, but doesn't seems to be the case of Yamato, simply doesn't have nothing to do on the boat... This could change being Momo's protector or some stuff like that... But ... Now doesn't seems to be the case XD
And don't make me laugh, here the anime isn't even considered as an adaptation, Carrot has been potrayed with the mugis on the anime hundreds of times, yet people here doesn't want to admit that could mean something, buuut i'm sure that now that you've mentioned that """Symbolism""" people is going to use it XDXD
Luffy DOESN'T EVEN KNOW IF THE ONE PIECE IS REAL OR NOT, teeling him about its existece is a huge spoiler for him. More spoiler if he talks about how Roger reacted, wich is a huge spoiler for Luffy.
2nd.
Yamato fighting Kaido now doesn't mean a shit when we saw Yamato fighting against Ace (Who wanted to freed the citizens) Yamato was against that Wano Citizens 2 years ago, now he defends them because he want's to sail out, he doesn't give a fick about them to be considered Deity (FOR THE MOMENT)
Yamato can easily see how bad has left Kaido the country, and try to help the citizens... Being a new Oden and a Deity...
4th.
Every Mugi has been presented doing some stuff related to their rol, maybe Robin was the exception, but doesn't seems to be the case of Yamato, simply doesn't have nothing to do on the boat... This could change being Momo's protector or some stuff like that... But ... Now doesn't seems to be the case XD
And don't make me laugh, here the anime isn't even considered as an adaptation, Carrot has been potrayed with the mugis on the anime hundreds of times, yet people here doesn't want to admit that could mean something, buuut i'm sure that now that you've mentioned that """Symbolism""" people is going to use it XDXD
4. The first two things Yamato did while talking to Luffy were: share a journal and say they want to fight on their side. Logkeeper and combatant, easy. Throw in guardian spirit for guardian of the Sunny, if you want. I really think the role argument is just a total underestimation of Oda's writing ability... I mean, we didn't need a helmsman for the boat until Jimbei arrived, but now it's critical.
Toei know more than we do. They spoiled Kyoshiro as a Scabbard, after all. That very same scene I mentioned was anime exclusive, and could have included Carrot, but didn't. Oda even commented on that exact episode in his comments for 1021.