Do you also believe that race is a necessary component for that similarity, or is it possible

Yup. Evolution doesn't stop at the neck.

I'm more curious about your attitude towards the cab drivers grandkid or great-grandkid who gets born in the US, gets educated, is less religious, etc.

That person will still be way too culturally distinct. We still see distinct differences in America amongst different white ethnicities that migrated here centuries ago, all of whom were already far more similar than the people migrating or being brought here now.

Or a black American, as they've been making an impact on what American culture is for a long time and aren't exactly immigrants

Most people over here are very much in favor of black nationalism. Muhammad Ali's speech on race and George Lincoln Rockwell agreeing with Elijah Muhammad are well known.