As for the former, I don't understand what you mean. Are you saying something like "there are fewer possible art compositions than rap songs, because art music is limited to 5-minute piano pieces"? That would be absurd, but I can't come up with another meaning.

What is absurd about it? It seems pretty apparent to me that rap can generate nearly-arbitrary sounds within the space of humanly-perceivable sounds, while Baroque/classical/classical-style music is limited to the smaller set of what pianos & flutes & etc. can generate.