Thanks for the answers. I can see how lyricists make sense for specific genres but for mainly pop music listeners this is not so much an issue; the composing process is rather different.
In general, I like to have composer tags as they can provide hints to cover or original versions etc. but I can see that it's of little use for people not interested in this kind of stuff.
I would think of using lyricist-tags if I could split the composer tags automatically but there is no way I would do that manually.
I still listen to music via Logitech Media Server and composers can be displayed both in the 'all artists' and in the 'song information'-pages of its interface. This is not the case for lyricists.
Well for Cohen, his contribution to the composition of melodies are not easy to discern and the contribution of Sharon Robinson, e.g.
here, remains unclear in Musicbrainz but I think we both agree that we listen to him not because of his melodies. . .