I think that's a bit harsh. In the case of the USA my impression is that the main source of cultural diversity is from immigrant communities whereas in Europe the main diversity is between long established communities - often at a level well below that of the current nation state (particularly noticeable in places like the UK and the other larger European states).
Personally, I think that Europe does have a lot more cultural diversity than the United States - but I can see that the point is arguable and that it's hardly a case of being "delusional" to argue the opposing point.
True, but then I'd go so far as to add that the USA is more diverse than any one country making up the EU.
And if that's the case, treating the USA as a comparable EU country in terms of diversity ignores that diversity found here. Which is what was being discussed in the first place.
I really did mean in area. The US dwarfs the EU nations. Apologies for using Europe instead of EU. I'd hoped the obvious context from the previous poster would help.
Still, I'd argue that the US is far more diverse than any single country of the EU, so treating the people of the US as all being the same is as silly as treating the people of the EU as all being the same.