All histories are revised by succeeding generations when people ask different questions of the sources. For me, Roud's book is a magnificent (revisionist) first step in making folk song studies relevant to the 21st century.
This doesn't negate what has gone before (shoulders of giants, anyone?).
Personally, again, it's the tunes and songs that I find most interesting, for their own sake, and the final sentence in Kathryn Hughes' review in the Guardian (here) sums up my views perfectly:
"These catchy tunes with their satisfyingly repeating choruses . . . . . are part of a landscape that is recognisably communal without being nationalistic. And as for the fact that many of them turn out to be as arriviste as Sharp himself, it’s not clear why it should really matter.".
P.S. I really enjoyed the book and I'm looking forward to a more leisurely read over the winter.