My point isn't that any particular generated song will be revolutionary. My point is that you can get any song you can describe. There will be billions of good quality songs made because billions of people will be able to produce a song just by describing it.
I expect new genres to be created almost immediately. And I'm not sure how real musicians can compete with that level of noise out there.
This only works if the sound and themes desired are vast enough for that. It's fine if a casual listener is a fan of something like anything house, pop, or electro. It's more difficult if your taste level is more obscure- a specific artist's style, or a specific juxtaposition produced from a one-off album. In that case there is quite literally not enough data to train on to produce further.
Even when there's not enough data to train on, it might still be possible to generate something in a desired rare style - provided this style is a mixture of several more common styles. Modern generative models are pretty good at interpolating.
Put it another way. If an AI could generate new Beatles music on the fly, making it sound exactly like the Beatles, with the same creativity of lyrics, tight harmonies, beautiful melodies, would Beatles fans go out in their millions to buy them? No. In the same way that the same dusty demos from the 60s found in an attic somewhere became valuable when it was discovered that they were Beatles demos. The music didn't change, it didn't get better or worse. The personal story attached to them was what mattered.