In this context I highly recommend Lockhart’s Lament: https://www.maa.org/external_archive/devlin/LockhartsLament....
Music is more or less taught as Lockhart describes in in the musicians nightmare. Art education isn't quite that dire, but it's close.
If you can't use a standardised test to evaluate somebody in a subject, it's of no value to the educational system.
Still, as Lockhart points out: at least art and music are recognised as arts. Surely even the ropiest music and art educations at least admit that these arts are:
1. ends in themselves, because
2. they are beautiful.