Well, this is why your stance seems to me dogmatic. The Steves are content to draw what limited conclusions they can from the available external evidence, and beyond that, they conclude that we don't have enough information to go on. In most cases there simply isn't any external evidence to decide whether a song pre-dates the oldest known printed version, and by how much, so they are content to leave the question there.

By contrast, you seem to be suggesting that in the absence of evidence, it's legitimate to simply assume an ancient and/or unique origin for folk songs that is distinct from printed sources. That is the step that strikes me as dogmatic.

I'm not quite sure why you think that Steve Roud's approach devalues folk song, or denies "the people" any creativity. It is certainly a travesty of his argument to say he thinks that folk song is "a commercial product manufactured for the entertainment of the people", as though there was a separate class of creators who simply imposed their output on the wider populace. Surely, all sorts of different people have been involved in the creation and transmission of different songs. Why do you feel the need to lump them together in crude classes like that? Why assume that there is a single mechanism behind the creation of folk song?