You haven't met many Europeans have you. Not all of them are Dutch, Scandinavian, urban youth or immigrants.
>a majority of them are not really all that good even in their mother tongue as we can see from standardized testing
This makes no sense. You can't be not good in your mother tongue - it's your mother tongue. Standardized testing has no say about how a language is structured, that's an absurdly prescriptivist point of view. As for foreign language ability, in real life it's not assessed by making them sit down and pass test questions, it's assessed by having them speak and write close to a native. Someone who casually uses slang, "bad forms" and occasionally makes native-sounding mistakes is more proficient at a language than someone who speaks an academic version of it and got good grades at a test.
Speaking three languages is not a big deal when you live in a village where everyone else speaks them.
>You haven't met many Europeans have you. Not all of them are Dutch, Scandinavian, urban youth, immigrants or throwawaybbb's great-grand-mother.
Also mastering a single language is harder than learning to get by in multiple languages, as even though a majority of Europeans can speak multiple languages a majority of them are not really all that good even in their mother tongue as we can see from standardized testing. They aren't worse than Americans, but they aren't better either, they get roughly the same results.