I'm not gonna pick a fight with you, but in the off chance that you actually want to have a conversation I will try to respond.
You're assuming there's a whole history of guardian deity devil fruits and the lands they're assigned to and a history of the people who eat those fruits being obligated to fulfill that role. Given Chaka's example it's certainly plausible.
However, none of this has ever been verified in the story. Specifically that obligation has only been mentioned by Kaido, and immediately rejected by Yamato. Furthermore, as if to rule it out further Momo specifically requests that Yamato not fight Greenbull so that he won't have to depend on her.
Unfortunately Oda's world is not deeply consistent enough for us to assume there's much more to the story than what he's told us. It's likely that he himself hasn't thought about it too much. He certainly has told us nothing else about these guardian deities. I suspect he only intended to bring it up in connection with Kaido's parenting expectations, as I mentioned before.
I just don't see the point of hanging onto this idea when it's mostly imagination, even if it's plausible, when there's nothing in the story that will allow us to verify it, especially when it's being overridden by recent events. Why waste time arguing about whether or not Yamato will become the guardian deity of Wano when it's going to become apparent in the next couple of weeks?