Nonsense. If both are fluent at the same level there is no difference at all.
That's the problem. How does an American become fluent in Polish? :)
The only ones I have seen like this lived in the US for years as children...and some of them have zero accent in English. More than a fair share rivaling natives though? I would disagree.
You are not in a position to disagree because you have no idea who I met and who the people were and how good their English was. You have lived mostly in the US so your experience is what it is but it doesn't prove anything in regards to my experience. In short, you have responded to a post you haven't understood or thought through. You certainly failed on the level of basic communication. You read the words and you responded using words but your response makes no logical sense.
Is that the alleged superiority of the native speakers of English?
English is not really that hard to learn. The pronunciation is a physical exercise and to be successful, a learner needs a lot of practice. The degree of phonological and grammatical fluency is directly related to the effort. Many people do not learn to become native speakers of the foreign language but to be able to communicate for specific reasons. Such persons will never speak RP whether they are taught by a UCLA prof. or by a half-asss teacher of English from Poland.
Again, I have met sufficient number of Poles speaking English with native proficiency before they had a chance to even go to the US or UK. Among them prof. Wiktor Jassem whose works are frequently quoted and used in the academia around the world. Another one is now the director of a teaching school in Poland, credentialed by British Council with the highest qualifications. He's specialty has been English phonetics and his English would put to shame many native speakers of the language.