Actually, the American Southern dialect

Individual dialects don't really apply to this type of generalization. That's really too specific.

I mean, that's a very specific part of America. Most of America doesn't speak like the Southern states. It may be the largest specific dialect grouping (I don't care enough to look into it more than a casual search), but that doesn't mean that it encompasses a majority of America. Boston also has an extremely conspicuous dialect for instance compared to the rest of the country, but we're not talking about Boston specifically ,we're talking the entire US generally.

We don't want to go about saying that British English is wholly determined by the specific dialect around London do we? Even though that's like 14% of the entire population of England.