The most obvious problem is that musicians can, and often do, interpret the instructions of composers pretty freely ... it changes from outside influences, which reduces the relevance of the 'creator'.

Yes they do. Don't see how this "reduces the relevance" of Mozart himself though. And whether it's a "problem" or not is up to the composer (and/or conservatories, critics, audiences, publishers, editors, teachers, individual performers etc etc etc).

You've described the natural course of events with any type of creation, I suppose. And it does correspond quite nicely, at a musical level, with the natural physical laws of random chance and chaos, with the biological/evolutionary mechanisms of genetic mutations, adaptations etc; and with time-honoured, universal religious/philosophical doctrines of free will.

I agree with most everything you;ve said though, so again wow and WHOOO-HOOOO Bill!   :-)

.............(Bill...why don't you just write a complete book and get it all out in an orderly fashion, and quit piling all this on THESE poor folks?)
...............(Oh, I really should, but I needed to start years ago, and I'm torn in too many directions...and besides...they asked!)

Yes! Go for it, I say!

Amos, ya got me thinkin (as usual!), so thanks ... and Bee, no, I'm not a 'Creationist', if you mean what I think you mean by that word.