I agree with most of your comment, but I do think you're discounting the ability for those hubs to exist elsewhere a bit. Dallas, Houston and surprisingly Atlanta all have really robust areas where you can see and feel the cultural influence of immigrants that live in the area.

It extends to the buildings that are built, shops that are run and overall feeling of the neighborhoods.

They're not all in the city for sure, and none of them are as big or as connected as areas you would find in say Orange County but still quite strong and really add to the cities themselves.