I do hate how he (and the whole generation, and some of the punks before him + no wave crowd as well) pretended that they didn't know any music theory or practice at all. That was quite destructive for so many of us who aspired to play music in our teens, especially if you weren't exposed to music theory and practice in childhood through other means.
I suspect this is true of many great songwriters, maybe even most of them. I would even argue that studying music theory may even make you a worse songwriter, because the most innovative songwriters don't seem to follow some clearly established rulebook, but rather they bend/break the "rules" unknowingly because their focus is on what they are feeling/hearing rather than something more analytical.
For example, McCartney tells a fun story about The Beatles traveling across Liverpool to learn a single B7 chord in their early days: https://www.youtube.com/shorts/_r5B1AhP1Fo
I was referring more to being well read in music theory in the academic sense. I am doubtful McCartney ever picked up a book on the subject. Traveling to meet someone so they can show you how to position your fingers so you can play a B7 chord is a bit different than that in my opinion.
Music - rhythm, harmony and melody - has patterns. Those patterns can be described / named. There are systems to also write them down.
When you mention reading / writing music and music theory, western notation and western music theory are what first comes to mind for most of us here. They are obviously not the only ways. Any one of us can trivially make our own systems, or adopt tiny portions of the western system. I have no doubts that people have done that.
From my personal experience, back we were teens, my friend group and I knew a tiny bit of theory (5ths, major, minor, 7th chords + pentatonic / blues scales) so we could use that in communication. The other thing we'd do is refer to motifs by citing them from songs, like "drum beat like When the Levee Breaks" or "strumming pattern like Where is My Mind). Or "for the brigde, turn it around like in Goddamn Lonely Love". Your group knows the same songs, and then you just cite that + show someone something on a guitar.
If you play with a wider group of musicians, a language likely starts to appear, and things get called fixed names more often. No doubt that all the blues people did it, the Beatles and that whole scene did it, ...
Now, if you're into music enough, and want to communicate with other musicians from different backgrounds and genres, it makes sense to just learn the regular western notation (because it's convenient for noticing harmony) and theory (because it has names for all the concepts). It's a bit infuriating that such fancy names ("dominant", "leading tone") are given to such seemingly simple things, but this is true of any jargon.
I've seen the equivalent with self-taught programmers, where they understand some CS concept, but can't name it properly. Maybe in your local demoscene, it got called something else, because nobody has formal CS knowledge. That was quite frequent before the internet, but still is possible when people do something as a hobby.
But for western music theory and notation, you can use it strictly descriptively and not prescriptively. Learn some, then transcribe your favorite songs, write down the progressions in roman-numeral-notation or something, figure out which scales are used, figure out how melodies fit over chord changes, ... Shame music education is closely tied to a classical (and / or jazz) repertoire in most places, it doesn't need to be.
But in any case, both playing well and writing songs obviously takes a lot of practice and effort, and you use whatever you have at your disposal to help. The "we don't practice, we don't care, this just comes out of our soul on its own" is plainly disingenuous, that's the most toxic part of it. But you can't write music without theory, at least your own pidgin theory.
there is a wall, on one side is everything that has been done.....and can be learned/replicated. If someone is compeled to see the other side the best way through, ha!, is with very little baggage/knowledge or theory
some few talk about the experience of crossing that divide, but in no way are they responsible for anyone else considering there museing, instructional
if you want a gentler discorse on the process, then there is no one better than keef, and his various atempts to explain why 5 strings are all he can handle, does alright with them as well
Theory can explain it after the fact, and can extend your options (or at least save you time knowing what you want). I know a lot of "untrained" musicians had a fair bit of theory, but I don't know about Cobain.
For the minor blues scale working over a major blues progression - I think the dissonance is okay because the flat third and fifth are often passing tones. If you loiter on them, they are more jarring.
But if you listen to a lot of blues, play a lot of it, play with other blues players, etc. You will notice there's a vocabulary, idioms, etc. You can learn them by ear. You can call them by names of songs or players (Bo Diddley beat), or by the number of bars, ... Well, all of that is kind of - theory. Also, knowing which things you wouldn't play because they don't fit the style, that's also theory.
