Different immigrant groups have better or worse outcomes, hence my saying "some immigrant groups". The cultural distance between the English progenitors of the US to the large wave of German immigrants in the 1800s is not as great as, say, that of Turkish immigrants to Germany post-WW2, or Syrian immigrants to contemporary Denmark.
Another way to look at it is that immigrant groups bring parts of their old world with them; German-Americans left a high-social-trust, low-crime culture and established it in their new country.
You can see this with Italian immigrants to America. I’m in New Jersey right now, and recently was in Wyoming. These are obviously not the same people despite being “white.” They’re more different than Pakistanis and Bangladeshis and we fought a war to be separate from each other.
> German-Americans left a high-social-trust, low-crime culture
Did they? I can't speak to the crime rate of the German empire, but a very common reason to immigrate, in addition to availability of farm land, was to avoid the draft (low social trust). The slow rate of assimilation is also a signal that these were not people coming from a "high-social-trust" background.
Another way to look at it is that immigrant groups bring parts of their old world with them; German-Americans left a high-social-trust, low-crime culture and established it in their new country.