It's a very fraught and fascinating issue. I have a few scattered thoughts on this, and I'll try to organize them into something coherent before I open my mouth. Preliminarily, though, I'm interested in your question:
The Pentacle Queen wrote:What does Brittens War Requiem/ Karl Jenkins 'The Armed Man' actually achieve?
Answering this question will depend on what we think the point of Big Issue Artworks is, and different people will of course have different opinions about this. Britten's War Requiem is a good example. The piece uses Wilfrid Owen's poetry as a running commentary on the traditional Latin requiem texts. Liturgical texts like
Lord, grant them eternal rest
and let the perpetual light shine upon them
are juxtaposed with secular texts like
What passing bells for these who die as cattle?
Only the monstrous anger of the guns.
Only the stuttering rifles' rapid rattle
Can patter out their hasty orisons
No mockeries for them from prayers or bells
in such a way that the secular texts seem almost deliberately placed so as to deflate and contradict the righteousness of the liturgical texts. If we assume that the purpose of the Requiem is to honor the fallen dead of World War II, then we might easily believe that the Requiem doesn't achieve a whole lot; we might even find the piece offensive. But if we assume that the purpose of the Requiem is to provide subjective commentary on the Big Issue being tackled, then we might be more inclined to believe that Britten's War requiem achieves something quite poignant: it shows us what wartime mourning sounds like from the perspective of a pacifist (as Britten was). Determining what the Requiem "achieves" is entirely dependent on what we expect to get out of an artwork that tackles issues of war and mourning.
Anyway, like I said, let me gather my thoughts a bit more....