It is an interesting divide. "German" is both an ethnicity and a citizenship, and it's possible to become one but not the other. "American" on the other hand is purely a citizenship, and so it is possible to become an American after immigrating.
This may be how you perceive or feel about it, and of course you're not alone, but many other Americans feel differently. Those of us with Colonial ancestors maintained much the same culture and mores for generations; it's evident in the manners and the literature; it's something distinct that we certainly feel as close to an ethnicity. Granted, we comprise multiple European heritages, but those heritages did not define any of us after a few generations. The concept I am trying to outline her is also a very old one: e.g., first Speaker of the House Frederick Muhlenberg, referring to some of his own constituents, said, "The faster the Germans become Americans, the better it will be."
I've had ancestors in North America since 1650, including a vice president and a union admiral, but I also have friends whose parents arrived from Somalia or Vietnam in the eighties and nineties who grew up in largely the same cultural soup I did, speak with the same accent, have the same humor, drink the same beer and eat the same food. Some have served in the US military. In my eyes, they're just as American as I am.
Europe the Germanic people have existed way before , a country is not tied to the ethnicity.
I’ve heard plenty of arguments about the German Volk as a distinct entity.
The argument was pretty decisively lost according to my grandfather.
Tell me, where does my Jewish German heritage fit in to Germany as an ethnicity? For some reason they didn’t feel very German when they left despite meeting all the qualifications…
That's a good point, and personally one of the reasons I disagree with the ethnic definition of "nation".
The other reason are of course the frisian, danish, sorbian, etc and many other similar minorities that have historically lived in the region of modern Germany.
I think the french definition (which defines the nation almost entirely around the language, not ethnicity or origin) is a much more interesting and useful one. Language determines who you can talk to, and what media you can read or watch.
There are many different distinct cultures in the US. Cowboys from north Dakota and Texas are both cowboys but have little cultural connection, and the hill billies Tennessee are very different from each.
But even that is too broad. It might be more accurate to get even more granular. For example, you might identify someone like Tim Walz as belonging to a synthetic Scandinavian-Midwestern ethnicity: although he has no actual Scandinavian ancestry, he grew up in Minnesota in what’s a recognizably distinct ethnocultural subgroup.
A far more useful analogy might be that “American” is a college football team.
"African Americans" certainly also separately underwent ethnogenesis, although the preferred nomenclature there has changed, and there wasn't really any disruption there. But I think it's certainly fair to count them as a distinctly and uniquely US ethnicity.