@Dragon-D-Luffy Yamato's arc, at least in Wano, was really all about Momo. She may receive more individual development in the future, but even the scenes where she shared deeply personal moments - like meeting Ace - were centered on Momo. That scene in particular was when Yamato passed on Oden's journal to Momo so that he could symbolically take up his father's mantle.
Oda could have used that Ace connection to underscore an emotional moment with Luffy, but instead used that connection to reinforce Yamato's growing attachment to Momo.
As you said, seeing Rebecca's role in the story as secondary to Kyros helps the reading experience with Dressrosa and I think a similar perspective regarding Momo and Yamato also makes sense.
This is something I brought up in discussing chapter 1051 as well - because for me, a big issue with the arc was the way Kaido was defeated. I actually like Gear 5, but the end of the battle itself felt abrupt and anticlimactic.
But Momo's speech at the end really drove home for me that this arc and even more broadly, story saga, has really been centered on Momonosuke. The big triumphant moment wasn't Luffy defeating Kaido, but Momo rising to proclaim himself Wano's new shogun.
Kaido was considered the world's strongest creature, while Momo first entered the story as a helpless eight year old child whose name ironically mans invincible. This was the story of Momo's odyssey through time and across the ocean to recruit allies he could lead into battle against the world's strongest. Luffy, the Minks, Law, Kid, the Akazaya, and Yamato were the soldiers whose loyalty was won over by Momo, who is slowly growing into the great leader he's destined to someday become.