> but as soon as they get good, then any human composition will be completely devalued

I think it will take many more years until an AI is able to compose like e.g. John Williams and play a score and sound like e.g. the London Symphony Orchestra. So there is room left for human contribution. On the other hand, the majority of humans even before AI was not able to value good vs. bad musical composition and performance, and instead satisfied with the commercial slop the market was flooded over the last thirty years. Studies of e.g. Spotify consumer behaviour demonstrated for many years before AI that more and more people consume anonymous playlists never caring who composed or played the music, just using music for its functional purpose like a commodity. It's depressing, but that's how society develops.

> a curiosity, someone who does things the hard way for their own amusement

That development already started long ago. In the eighties and nineties, music schools florished and children wanted to learn instruments and play in bands or orchestras. That completely changed over the last thirty years. Musical instruments will be a curiosity in a decade or two people are going to watch in a museum, wondering why anyone would have learned these skills in the past.