"Some of MacColl's songs, to my ear, bring it off"

Not to mine, at least as folk music though he wrote some decent pop tunes I admit. MacColl's stuff sounds more of an accompaniment to the 1950s Angry Young Man cycle, Osborne, Braine, Sillitoe but then so much of the revival original material does.
I agree with what you say about traditional music being pre-dated WR, but that sets off alarm bells that what we're really talking about is aesthetic choices retrospectively wrapped in theoretical trim until the ribbons and bows - the sound, the ambience, the aesthetic - are what really attract people after they've forgotten the music of the people inside.

Modern sensibilities can't really write about Men O'War or Hard Times on the Farm without tongues well into their cheek, so I fear SO'Ps 'wrung what yer brung' may well be what folk music really is when you get beyond the period detailing.