Effectively Art music and singing, and Traditional Folk Singing have their roots in the same tree. The 'trained' voice for the concert platform, is no more trained than the Traditional Folk singer at the height of his powers. Some of the vocal techniques are very similar and the breathing techniques are also of interest.
When I am faced with a Tweedle dum Tweedle dee argument on singing styles (which does happen), I usually end it by suggesting that the protagonists firstly listen to Harry Cox singing Seventeen Come Sunday, and then Pop Maynard singing 'Polly on the shore'. Then I issue the challenge as follows. Sing along with either song, and take a breath only when the singer does and see how far you get. I still need an extra breath on the Harry Cox song. Finally get a musical instrument, play a note, sing unaccompanied for a few verses, play the same note and see if you have shifted. Then test Harry Cox the same way. Find the key he is using and test his pitch. It's bang on every time. The equal of any 'Trained 'singer.
End of argument for me.