the people the rockist disapproves of are supposedly making music for the Man rather than for the Muse

Perhaps I can fudge my definition to include the intended audience under 'meaningfulness'? I didn't define that above, but it could be expanded just like 'artist input' could be. 'Meaningfulness' could cover not just what the artist is trying to get across, but to whom (if anyone) they are trying to get their message across, and why.