The above is utter elitist pish. So what's the difference between "mimicing what you have previously heard" and "mimicing" what's written down on a piece of paper ?

"If somebody can read music and play a musical instrument, if somebody can read music and sing, then either can be given the sheet music of a piece that they have never, ever seen or heard performed before and play, or sing, that piece exactly as the composer intended it to be heard".
How can you possibly know that, especially in terms of traditional music ? You give a sight-reader a piece of paper and they will play what's on the piece of paper, which may or may not be by the composer. You seem to totally disregard the concept of individual interpretation.
Amazing to think that Irish traditional music was kept alive and is in the healthy state it is today largely thanks to people who weren't "musicians" because they couldn't, or chose not to learn their native music from a sheet of paper.