Let's remember that music theory isn't universal to every culture in its intricacies. We speak of western music theory while ignoring eastern and middle-eastern theories. Indian music theory, in particular, is so detailed that they have guidelines for harmonising microtones.
As an aside, any serious student of music leans scales and chords that specifically break what are considered the most proper scale and chord forms. Think the harmonic minor scale, which can be baroque or eastern depending on how you use it, or the phrygian dominant (a sort of cousin to the harmonic minor) that, while technically a major scale, works melodically much more like a minor scale.
Note that most scales have more scales derived from it, equal to the number of notes in the scale itself. There are thousands of scales. They all fall under "music theory" even if the vast majority of them actually slaughter wholesale "proper" classical harmony.