For further research the standard terms may be useful: Program music vs Absolute music. Program music, which is probably what you mean by "narrative music" is music that tries to describe something besides the music, and absolute music is just the opposite in that it is music that it doesn't aim to portray any story.
Given that all songs, oratorios and operas belong to the former, this can be hardly considered as niche repertoire.
I see there's no difference of quality, but your mileage may vary.
