I think we can easily extend the argument to singers. In fact, I think it's more obvious and clear when we do.
Imagine soon, or maybe even already, we have an AI that can mimic any musician's skills with new words. Then, you go to see a singer. But what actually happens is the person on the stage says "here's a song I wrote as it would sound played by Eric Clapton".
Then they press a few buttons, and there's a really good rendition of their words as if Clapton had toiled for several weeks creating new guitar riffs to match them. It's brilliant.
But... you came to hear a singer, see a performance. What you're getting is music, without any of the effort. It might be a good show, but it is not a live music performance.
If this happened, and the event had been sold as a live performance, most people would be rightfully dissapointed.
Songwriting is quite the same, except that it's hidden. We don't see the writing happen, we only hear the result. With a live performance, the (artist's effort)/(audience feedback) loop is immediate. With tasks like songwriting, or painting, or writing novels, the loop is delayed.
The delay matters. People will care a lot less if they don't immediately see that the effort was made by a computer rather than a human. Even if you tell them later, they won't care as much. The human psyche gives huge weight to immediacy. But I would argue there's no difference. If you appreciate the artistry and effort of seeing a human performing live, you should try to extend that to appreciating the effort of an artist who toils for weeks or months behind the scenes before showing their work. Otherwise you're saying that live performance is somehow a more valid form of art.
This is not an argument against AI art or music, by the the way. If the show, the painting, the song, or whatever, is clearly labelled as an AI creation rather than a human artist's, I have no problem with that. However, we are alreading seeing efforts in the film and music industries to remove humans and replace them with AI. It's starting with extras but as the tech improves it will move on to everything else. The big studios would love if they can get away with that. I don't think this is a good thing.