> The conventions were discovered first, music theory came after composers did things.

Broadly completely untrue.

If you're trying to say that humans were making music before we had a theory for it - absolutely. But every advanced musical tradition on the planet (including Western, but also Indian, Chinese, etc.) has developed alongside a system of analyzing that music, and for very good reason: It's a lot easier to teach music when you can actually talk about it.

I promise you, every single competent composer and musician on the planet - from every culture - has a fairly firm grasp on music theory, in whatever flavor is relevant to the form of music they practice. Every Indian musician who plays classical Indian music knows their ragas. Every Western musician can navigate the diatonic scale.