From 2006:
So which part of the G & S operettas is more important, the words or the music? My Solomonic answer is that the musical numbers–which are, of course, by Gilbert and Sullivan–are vastly more important than Gilbert’s facetious libretti. As for the songs themselves, I’d say that Sullivan is primarily responsible for making them memorable, but that Gilbert’s words were primarily responsible for inspiring Sullivan to write such memorable music….
Read the whole thing here.