My take is this. Theory is just that, a theory. It is not fact. It is a way of taking the Western music's division of an octave into 12 notes, and trying to write rules about what sounds good to most people when you navigate those 12 notes. Play Indian music and you will have a whole lotta new theory to learn because of their different division(s) of the octave into more than 12 notes. Other cultures have done the same. Heck, even in Western music, some composers have decided to divide the octave their own way, including Ivan Wyschnegradsky who created 24 notes between one note and the octave above, and Harry Partch who tore up the rule book and composed 43 different notes within the octave. My point is, theory is there to give us a set of guardrails in the music we create so we don't go over the cliff, best I can tell. But some want to go over the cliff and more power to them IMO ;~)) Does not mean I will listen to it, but nothing wrong with it as far as I am concerned. And some want to stretch beyond the popular genre and create more complex material, more power to 'em!
Now that said, the "what sounds good to most people" is also of course subjective (and it is not up to you, it is up to the record companies and streaming services to decide what to push on people). If I play something that I like, and it does not fit in with some theory, IDGAF. But if you want to attract the masses, you have to generally play within the confines and with the scale/notes provided to your cultures "theory". Given that, we already know that "good beat, easy to dance to, I'll give it a 98" is how most people think. The masses don't care, IMO, about how complex a musical piece is or whether it violated/adhered to some academics theory of what should have been done. They want a good beat and a catchy phrase/melody that they enjoy and want to sing/hum/dance along to. In that scenario, like Lou Reed said "One chord is fine. Two chords are pushing it. Three chords and you're into jazz.". Now he did not live by that rule (unless you want to call most of his work jazz), but you get the point, it does not take complex theory to make good music, especially rock n roll ;~))
If you want to create something beyond rock/pop music, theory has it's place and will likely help you to do so, and some won't even need it because they are naturals. And even rock/pop music can be complex, but generally speaking it is not as far as I know. And even in rock/pop, there is theory at play, but nothing that requires any intense study IMO nor should anyone feel intimidated or ashamed by the simplicity employed to make good music. Look at the Beatles, CCR, Steve Miller, The Rolling Stones, Bob Dylan, Tom Petty, Buddy Holly, country music, etc. Yes, in many pieces you will have elements that have more complex things going on, but the basic theory of so many of the most popular songs ever are VERY simple. There is a reason why jazz and classical don't have a huge market share in the music sales and concert world, it is because most people don't want to be challenged when they are listening to music, and often both of those genre's will challenge your mind to follow and keep up with what is happening (because in part of the more complex elements of music theory being employed). The more complex it gets, the lower your audience numbers will be IMO. Does that make it less valuable? From a monetary stand point yes. But from a "pushing the boundaries" standpoint, it is essential. I LOVE a lot of jazz, and I ain't talkin' Kenny G. I love some classical. Prog rock is one of my favorite forms of rock because of it's complexity and the "beyond normal" elements it brings to the table, but none of this makes me think that in order to create good or even great music, one needs to become well versed in theory. The better you understand music and it's theory, the easier the task of creating music will be for most, but the depth you need to explore theory is a whole other question and I don't think you need to be in the deep end to be a good/great musician.
So KISS (Keep It Simple Silly) and make (up) music. Let the academics debate over the theory and the geniuses create the complex stuff. For the simpletons like me, just keep on keepin' on doin' what sounds good and try to not go off the cliff ;~))
