"....or a traditional flute player joined an orchestra and insisted on putting traditional slides and slurs into a classical piece."

If you're referring to wooden open-holed "simple system" flutes, those used to be the instruments used in classical music - utilizing slides and slurs, and variation at the whim of the player. Classical music has changed over time as well.

I agree with you all the way about Sean Ma/Mcguire, Geoff. Have always had the same take - great virtuoso when he goes easy on the Heifetz touches. Can't much enjoy the sobby airs either, although I was pleased to figure out the other day that he was playing Our Highland Queen on one of my 1966 recordings.
Andy McGann was a great fiddler and a student of Michael Coleman's, who Andy said preferred to just play music instead of talking about it ad infinitum.