You want to morph the definition of the derisive label you apply to people to fit your desired end, but you still don’t get there. A) It doesn’t matter if your definition of “Yankee” is making the food. They’re still exposed to it regularly and have the resulting palate, and B ) yes, many of them are making it and have been for generations.
The pizza in NYC, Chicago, and Detroit blows anything away that the South has to offer. A chopped cheese in a NYC bodega. An Italian beef in Chicago. Boston seafood and chowder. A fried pork tenderloin sandwich in Indiana. Philly cheesesteak. Primanti Bros. in Pittsburgh. And yes, ethnic food in northern cities blows ours away and many of those restaurants/families have been there for generations.
We’re actually pretty food-limited down here compared to those places. And if you start counting other places outside the South, but not “the North,” like Seattle, New Mexico, and San Francisco, the gap grows even more.