I would say after a couple of generations most American families become more American and less whatever culture they came from. Especially in generations past, and depending on where they're from. I grew up expressly American. On one side English heritage; the other side German, but this mattered not a whit. Just a pure American upbringing. We have a culture and make no mistake about that.
There's certain things that come with the American way of life, thats for sure.
In my experience, culturally anyway, the foods, holidays & traditions seem to maintain the influence of the family's roots.
That can get eroded over time, depending on the fabric of the family and how they decide to keep up with things or not.
After being sport, food and media-centric ~ Americans seem pretty diverse to me.
There's still a thread that connects them.
Perhaps I, as an outsider, can observe this.
Probably as an outsider.... you don't spend 365 days a year inside of the households of 100-ish plus hoardes of friends and families, over the course of decades, within communities on teams, boards, festivals and crafts, in order to glean the most accurate picture of things.
There's a charicature that would be easy to paint of American Culture, thats the "thread," but its not the ethos.
I've done all those things you describe.
But I'm not into a game of one upmanship with you.
Oh you've lived American culture for decades, have you?
Thats interesting, because I couldn't really expect a single male American to agree with this OP. Why might that be?
Oh, I dont know 2 obvious reasons might erode her over-confidence in trying to postulate a stereo-type for the Country where one does not exist:
1. Folks in NYC act 180 degrees different than folks outside of that City. In America, this would be classified under "common knowledge."
2. Pretty much every guy I KNOW has a different way that he treats women from the last guy. It would seem an unrefined view of things to postulate that there's some norm, there. We have everything from Gentlemen, to snobs, to players to betas who let their woman control them. Theres HUNDREDS of types of American guys when it comes to their treatment of women.....not 1 predominant one, save for theyre mostly polite.