Right now the musical theatre guidelines especifically say “the release group and release artist credit should be to the composer(s), rather than performer(s), lyricist(s), or librettist(s)” - before going on to list five famous exceptions where the lyricist/librettist should indeed be added to the AC anyway.
Classical and soundtrack releases don’t specifically block lyricists or librettists, but they do specifically say to use composers.
I can see no good reason to block credits to lyricists and librettists if they’re who the release actually credits. This seems relatively common for musicals. While outside of musicals, librettists and lyricists being given credit for a release is less common, I’ve definitely seen classical releases with, say, songs on Verlaine or Shakespeare poems exclusively, or operas where the librettist also gets a prominent cover credit.
Is there any good reason not to allow adding those as artist credits?
I agree. It’s not something I’ve given much thought, because I’ve always just credited whoever is credited on the release, though that’s rarely the librettist.
Especially for musicals (and theatre?) I think we should use “writer” rather than “composer” explicitly.
In fact, for a short time, it was common that soundtracks were credited to composer + lyricist (see the “Hair” musical’ edit-history)
Soundtrack: changed composer to writer for release artist. Left composer for track artist, because it still seems reasonable to me as a default choice, which is how it’s used there. (diff)
Theatre: removed the prohibition to use lyricists / librettists when they’re credited. Changed “Exceptions” to “Standardised collaborations”. Do we want to keep those standardised specifically as “Surname & Surname”? (diff)
Classical: changed composer(s) to writers for release artists. Left most other mentions of “composer” since it’s still what’s relevant most often for the examples. Similarly, I didn’t touch track artist since when relevant, I’d expect that to still be set to composer only. (diff)
I haven’t transcluded the changes yet (they’re only on the wiki). Feel free to suggest any improvements or corrections in the next couple days!