He is quite formidable, he dazzles me by way of posh words but I don't either make up the past events nor mislead you about the current Japanese verbal system.
All what I have to stress about this is the fact that the head of new administration was implacably an emperor who didn't speak somehow Yamanoteben...or whatever from"its begining".
Attention. From its begining;
I mean it was the time to establish the new foundation for unified verbal system. then, why they ruled out the speech from other district in spite of defeating former Edo administration? This is why I insist that they designed the current verbal system as they want to.
Do you know the fact that Edo period lasted at most quarter millennium until it ends, in contrast to the 2.5millennium reins of imperial house at that time?
The dynasty stayed in power around Kyoto nearby almost 10 times as long as Shogun's in Tokyo. That was overwhelming. Then why they ruled out? That's because they obviously excluded it on purpose.
Some immovable reason for consolidation might exist, but they did't understand what it cause in later; It ended up proliferating the "entitled" people(they are literally bad cancer.) who believe the royalty of their speech with no respects on other native speeches in the vast areas in Japan. They are still not sure why they can be such confident. That is all the people in Tokyo about.
And this is the messege for you from the bottom of my heart;
"If you see some dialect in an answer which you get, please don't rule out or ignore it. they are reach out to you hoping to pass on their native speech. They are not very abnormal."