Thanks so much for the comment! I learned quite a bit from it. Although, I may still argue that last point.

To clarify, are you saying there's absolutely no creative reason why a song's lyrics should ever be illegible? Is humming not music of a sort? Or am I misunderstanding the stance you're taking.

Certainly, not every instance of cloudy lyrics is some profound attempt to be more expressive, but at best I'd certainly argue that ambiguation can have that effect. And that many artists, when presented with the option to enunciate or not, might creatively decide not to. I don't see why that's wrong if that's their creative impulse.