Not to quibble, but one frequently hear of literary, mathematical, scientific or other conceptual/cognitive/artistic achievements described as virtuousic, no? It seems unreasonable not to allow for composers being described as virtuousi along the same lines. (Bach's composing a six-part fugue on the "royal theme", Mozart turning random melodies derived from rolling dice into perfectly formed minuets or completing the Linz Symphony in three days, or Bartok finishing the Divertimento seem like pretty good examples to me.)
John