Jim,
I can find very little to disagree with in what you have written here. The fact remains that current academic and scholarly study puts the published corpus of traditional English folk song down to commercial origins of some sort. However, ultimately the origins of any creation cannot be proven and that includes Shakespeare's plays and many other works of art. Sometimes you have to simply take the word of those who have studied the material in great detail and come to these conclusions of origin.

Double standards. The agricultural union short-lived songs are folk songs but not my farm hand who wrote songs about his farming experiences?