> Here[2] Is the syllabus for ABRSM Grades 1-5 music theory.
I've always thought that's mistitled. Better would be Traditional Western Music Notation Theory.
Notice what's absent, e.g. frequency and timbre which are nicely introduced by the current article.
Music theory is a lot wider than the ABSRM syllabus. And the current article is a great starting point.
Done on purpose. The assumption here is that this theory is the one and only theory.
That's sound design theory, not music theory. They're not the same thing.
Music theory is about chords, scales, rhythm, and - most importantly and elusively - how to fit them together to say something interesting.
Entry-level trad Western Theory gives you the concept of a basic grammar as a first introduction, but once you have that you can extend it fairly painlessly to jazz/funk/metal/pop/whatever.
Advanced classical grammar - baroque and modal counterpoint, extended harmony, and such - has some useful pointers for modern song-writing, but it's a specialised skill for experts. Movie and game score composers likely know it, but it's a degree-level skill.
Sound design theory is a subset of orchestration. The proof is that you can take most music and play it with simple sine wave bloops - no orchestration at all - and it remains completely recognisable.
Explaining equal temperament etc sounds clever and it's interesting if you like that kind of thing, but it's a distracting level of nerdery that doesn't help at all with basic song writing.