It is about shaping the tones, orchestration, what is it going to do next?
A person could be given a sequence, which could have been from mozart lets say, the strength and skill of the composer to wield that sequence is what counts. Obviously the better composer will show, if your working with a Schoenberg sequence or a Mozart Melody, they pretty much are the same thing.... :D .....with slightly altered theories. Schoenberg was asking the question, why are these the tones that you chose? Basically, in music we have built a system, and to deny Schoenberg's or anybody else's as being better is futile.
Like I have said before, we are putting 18th century ideals into 21st times.
If the music was purely mathetmatical then a computer would do it, and we wouldn't have composers today that slave away.