I'll hold out for a ballad being a song with a narrative. IT can be traditional or not, good or not, authentic or not, popular or not, broadside or not, but it at least provides a useful grouping for a class of song. Obviously one can be more specific. simply by applying an adjective (modern ballad, traditional ballad, Child ballad etc.) but it's useful to have a generic word to distinguish narrative songs from , say, lyric songs or dance tunes or chanteys.