Fully absent from your consideration is the fact that both Austria and Germany are part of the EU, a project in diversity maybe only outdone by the indian federal state.
[1] https://en.wikipedia.org/wiki/List_of_sovereign_states_and_d...
[2] https://en.wikipedia.org/wiki/Islam_by_country
[3] https://en.wikipedia.org/wiki/List_of_political_parties_in_G...
And EU diversity isn't anything like American diversity. Your countries are nothing like our states, our "mixing" is a lot higher.
The US has to solve problems of a kind and at a level Germany and Austria will never have to deal with. The scales just don't compare, it's laughable to even try.
[0] https://en.wikipedia.org/wiki/List_of_countries_ranked_by_et...
I was wondering if this might be because most immigration in Germany is actually from more or less neighboring EU countries, and according to [1], that group accounts for 2/3 of the immigrants.
[1] Figure 2: https://www.bamf.de/DE/Themen/Forschung/Veroeffentlichungen/...
My worry for you is that this reaction is a visceral one, fundamentally rooted in a dislike for America's diversity.
It's a messy process, getting everyone to work together, and we're fucking it up pretty monumentally, but to call the effort a "shithole" seems like you'd prefer the US be less diverse? Fewer disagreements would arise, but at what cost?
Germany and Austria have... less than stellar records when it comes to human rights, and aren't exactly known for their exploding levels of diversity on a national level, so perhaps the "unity" you're experiencing came at a cost? Perhaps that very cost was something that disgusted you in the US?
I wonder how a Muslim would describe living in Vienna vs. living in, say, Chicago or DC.