[bkazez]

This is not true.

Singers and violinists can and do adjust intonation so each chord sounds (justly) in tune. The exception is if they were trained with equal tempered instruments (which is common nowadays - see Duffin, “How Equal Temperament Ruined Harmony”) or if they are playing with pre-quantized (fretted/keyed) instruments, in which case they would match the existing temperaments.

So the linked article, while it shows some beautiful shapes linked to 12s, has nothing to do with actually (justly) in tune music.

Source: master’s degree in the topic; am a professional singers specializing in music written before equal temperament was invented

[Tor3]

I go to a lot of choir concerts. What I've found is that I much prefer (good) choirs singing without accompanying instruments, because when there are instruments involved the harmonies always fall into equal temperament. There is a quality when they sing a cappella which simply isn't there when they don't.

[tugu77]

For a professional musician you are oddly singer/violin focused. Any instrument which can physically detune while playing has their musicians do this. On wind instruments it's via the mouthpiece, any string instrument beyond violin has some flexibility etc. It's only the piano that doesn't, essentially everybody else does.

But in practise, for many music styles, it doesn't really matter. Music is so much more than whether some chord is pitch perfect in tune.

Source: Jazz musician on 6 instrument types part time professional for 25 years (other part is software engineer).

[PaulDavisThe1st]

I did speak a bit loosely and too simplistically. What I was trying to get to was the point you're making which is the same point the GP was making: when performers have the ability (because of the instrument they are using, including the voice), they will adjust to reduce beating.

My words on this were wrong and misleading.