Implied in some thought about - shorthand - western classical music seems to be a descendant Platonic argument, that sound is inessential. It's strange how it persists, given that I don't imagine many would now claim that language is external to thought (have there been theoreticians who have dissociated colour and line in painting? Or dematerialised sculpture?) People used to say things about Bach being 'abstract music', despite the wonderful sensuous instrumental effects and affects in his music or his fascination with out of the way musical instruments and with instrument technology.
I wonder if there's also an implied thought that if anything is an arrangement it is performances involving the instruments Bach had to hand, or copies of those instruments (or Beethoven in this case) - the music was waiting for the perfected instruments of the modern orchestra to sound correctly (which is to say, to sound as Music rather than sound), and the music as music implies modern rather than reconstructed 'historically informed' playing techniques to emerge as Music. So that in a way modern instruments are atemporal and disappear as a medium and ditto modern techniques which are themselves pretty much fixed and un-extendable (or are restricted to being a transparent medium which nonetheless sounds beautiful and right).