Interestingly enough, it wasn't necessary even after the "Folk Scare" to have a rock soundtrack to make a huge hit. Didn't happen very often. But Judy Collins had a huge hit in, I think, 1969, with "Amazing Grace"--and no instruments. Only "gimmick" was the chorus backing her up. Admittedly it was just amazing at the time that it was such a "pop" smash.