I don’t mean to contradict you, but I want us to in this discussion hold on to that Brian Eno assertion of himself as a non-musician. Indeed, Brian Eno has had no formal music theory training, and his whole schtick for saying so is that it’s not necessary.
And I strongly agree; music theory training is not necessary for making beautiful, even harmonic music.
I’ll defer to some of the good people you mention in your post to talk about their process more if they’d like, but maybe I’ll share a challenge I’ve had when writing music. (It’s actually something I’m still negotiating.)
I have an undergraduate degree’s worth of classical training—so both more than some on this forum but definitely less than others. I also love pop music. When I was studying harmony and voice-leading, I noticed that whenever I would try to follow the prescriptions of my textbook to the letter while trying to make pop or dance songs I would end up with something that sounded way too “cheesy”, for lack of a better word. This bothered me, so I spent actually a good amount of effort trying to understand the chords in songs that I really liked and how they fit together and I realized that maybe they were following some music theoretical rules, but they weren’t rules that I was going to be taught, so I would have to learn the rules of “pop music theory” by studying songs I liked and trying to see what sounded good.
my point isn’t to toot my own horn at all, but just to say that I used to have this conception that if I could learn some rules for how to fit notes and chords together, I would be able to write good songs. I learned “the” rules and I still couldn’t write a good pop song with them. Now my thinking is more along the lines of learning what sounds good to me by trying a lot of different approaches.
I put “pop music theory” in quotes because my perspective on this is that theory follows practice. I bet you that Brian Eno is far from the only musician working today whose knowledge of music is more experiential (“that chord progression sounds good”) than theoretical.
I’m excited to hear more perspectives!