This is an interesting read but the article cites no sources for its claims. Even the claims that refer to linguistics debunking other theories have no citation. It also makes some suspect statements. I live in New England and saying that it is hard to find someone who does not have an accent that links them to some New England locale is just silly. Then there is the claim that the “general American” accent heard on…
Hopefully a linguist will come along with better treatments of the subject, but Google turned up a couple of articles with more links:
https://curiosity.com/topics/the-american-accent-is-older-th...
http://www.bbc.com/culture/story/20180207-how-americans-pres...
And, of course, there's Wikipedia: