All right, a follow-up question: would you consider any (Most? All?) works in the Theme and Variations field to be arranging, rather than actual composition?
I believe there's always some composition work involved in arranging, but Britten, Brahms, and Ives are also master composers, something Sir andrew will never be, and the Theme and variations situation is a knotty one. As opposed to arranging "Moon River" for Liz Callaway, which is a simpler job of composition and arranging, Rachmaninoff's Variations on a Theme of Paganini is a masterpiece of composition, as are Brahms' Variations on a Theme of Haydn, the Ives, the Britten and others. Others I love are Mozart's variations on "Ah vous dirai-je Maman, which Dohnanyi also used in his piano-orchestra variations. However, Beethoven, Britten, Haydn, along with Vaughan Williams, Holst, and others also arranged English folksongs, all different and all interesting, and all involving compositional skills (Britten's "Ash Grove" succeeds a lot because of Britten's bi-tonal skills in handling the emotions of the song). Brahms arranged German folksongs, even wrote a song for mezzo-soprano and viola based on the German carol "Joseph lieber, Joseph mein." Now I'm rambling. does this make any sense?