An artist writing their own songs is great. But that artist isn’t somehow more authentic or worthwhile than someone else who doesn’t.
A piece of music that stands the test of time hasn’t done anything except exist for a while. The test of time is no test at all.
Some music feels synthetic or manufactured. But all music is manufactured. Some music is manufactured to feel less manufactured than other music. Grunge is no less manufactured than hair metal. If it feels like it is, you’ve revealed your aesthetic preference.
There’s more to music than just Western music theory. It might be hard to see that sometimes, especially if you’re embedded in Western culture. I might say that the internet should allow you to more easily experience other cultures, but it also extends Western cultural hegemony, so maybe not.
Music isn’t harmony, it isn’t melody, it isn’t rhythm, it isn’t lyrics, it isn’t instruments. If a particular type of music is missing one of these things, it doesn’t make it less musical. If you feel like it does, you’ve revealed an aesthetic preference.
Aesthetic preferences are fine. But in the end they’re just preferences, a sort of lens that you use to look at music. Or, to put it another way, a perspective. That you have one perspective, or even that a whole bunch of folks share your preference, doesn’t make your perspective right, or normative, or inherently valuable.
You can’t tell what music ought to be by looking at what music is.