"Most of the tunes played in the 'Anglo-Celtic' tradition have their origins in countries neither Anglo nor Celtic"

Most of the tunes?
I have to seriously question you on this and ask for a whole lot of examples. There is an identifiable musical tradition (or set of overlapping traditions) in the British Isles that has strongly influenced American folk and popular music. As for French and German influences, I have to ask you to give examples as well. And I don't mean a few tunes or transplanted instruments, but a substantial body of material clearly traceable to continental Europe or elsewhere (and no trans-galactic theories, please). At the same time, you'll have to explain why these influences you argue for are linear and uni-directional. Everything I know about music tells me that musical diffusion between cultures and regions involves give and take.