Foreign born includes Danes and Norwegians so trying to disprove the claim that Sweden is socially homogenous by pointing out that there are Finns and Danes, doesn’t make your argument convincing.
I think what makes a comparison difficult with the US is the difference race and ethnicity make between countries (eg, Sweden and US). In the US there are many negative correlations with race and ethnicity that make diversity comparisons simple to make (although not necessarily accurate). So people can easily look for diversity by just checking race demographics. It’s also difficult because some people talking about race are racists who have incorrect beliefs, but it’s hard to tell who’s who at first.
When looking at Sweden it’s not straightforward to look at race and I couldn’t even find solid numbers that describe Sweden by race, although only spent a few minutes googling. But in the US, racial demographics are immediately available.
If you compare nation of birth != Sweden that’s not necessarily useful comparing to the US as it includes other culturally similar peoples (eg, Norwegians). It would be like saying New York is diverse because it includes lots of people born in Connecticut while not breaking out those born in Somalia.
The comparison that is relevant is what are the diverse cultures, specifically those from lower socioeconomic status. Unless you can check that mix, then it’s not very useful to compare and make claims.
Of course, the purpose of comparison isn’t to achieve some sort of purity goal, that’s insane. But to identify what interventions are most effective based on cultural composition. While theoretically a country would higher social cohesion by getting rid of all the different peoples (Denmark pretty much did this is WW2 with the help of the Nazis). This is short sighted (hurts World to help country) and immoral (genocide is bad).