My post was made over a week ago and now it is resurrected as new.
Did you as moderator do that to highlight your response?

Trouble is with 'American English' is you can run out of English.

I understand your meaning. But poorly written English is certainly more of a barrier to communication than native language place of birth.
There are countless 'British oral English'es and 'American oral English'es. No doubt the difference between Liverpool and Las Vegas is larger than the difference between Liverpool and Manchester or Las Vegas and Manhattan, but there is no unitary national oral language.

I doubt that the size of oral vocabularies of a language differ more by nationality than by individual. Perhaps Turnoi can enlighten us here. I also believe that there is also a rich and significant inventory of regional oral innovation in the United States.

Written language is a completely different field of endeavor; I don't believe that I write in American English. And I recognize that some people choose to mimic oral language in their writing. See your sentence above. I do not think there is anything wrong with that, but it can compromise precision of thought and lead to misunderstandings among readers that do not have the same oral tradition.

I admire and respect the written output of all writers of English, regardless of their place of birth (which is why I am offended when Churchill is misquoted).