These days a lot of them can't actually sing without autotune to clean up their caterwauling.

Still artists.

Yes, I'm not complaining that Tina Turner or Diana Ross didn't write the songs they sang (with the odd exception).

I'd say they are performers not artists. The girl running Photoshop is an artist, the HP LaserJet that prints it out isn't. We don't consider choir members to be artists, but if it's just one voice we assume they are?

The performance is the art. In your analogy printer = PA system.

Who doesn't consider choir members to be artists?

Members of the choir are performing artists. They make artistic choices related to the actual performance of the song, like how to sing the words written on the page.

Members of the choir do not make those choices. The conductor does. The singers are the instrument in that case. Like a pipe in an organ. Their job is to blend and produce the sounds according to the interpretation of the conductor. Source: am a choir member. You will be fired if you interpret the music against the conductor's desires.

Now you're just getting into a war about what art is.

If Jascha Heifetz and Murray Perahia aren’t artists then your definition is theatrically absurd.