Might? Is.

I'm not there yet.

Where do you draw the parallels?

Because all songs tell stories and give opinions in the lyrics.

Not all songs have lyrics.

But they do convey a mood.

You're right though. They all do tell stories. You can hear the rising action, the dramatic tension, the climax and resolution.

You can even find expetions to that... Some songs are just like a steady river - meditative music.

I see where you're going.
I've tried to tackle it from a logical view.

If all songs are opinions - does that mean there is no objectivity in music?
Since music is also art, I would say: Yes, probably.

I thinki it's also hard to make general statements about all the different music genres out there.

It's also difficult to categorize certain artists.

I've found John Denver in Country, Folk, Easy Listening...

Enya in New Age and Celtic...

The borders are very vague.

It is. And I find it generally acceptable to say: Some artist is A, BUT ALSO B.
...instead of inventing new terms all the time. Although the bands and artists might understandably like it, cuz it often makes their unique selling point.
My former band for example made medieval-themed Metal music. And they/we coined the term "Metalalter", which combined "Metal" with Mittelalter (german: medieval era).

For the writer or for the listener?

I would agree with the therapy part.