On question that you did not answer - Can people with mediocre talent who put in a lot of effort become professional musicians / songwriters etc?
Anyone can learn the basics of songwriting. Analysis of hit songs alone reveals tried and true formulas for rhythm, lyrics, melody, chord progressions, bridges, etc.
So, the average guy could take known successful strategies, pull out things almost randomly and produce a listenable song.
But without the innovation and out of the box thinking true talent brings, those songs are gonna sound both familiar and average. I have a bit of talent, but I'm not at the level of composing stuff that would interest others.
If by professional musician you mean the simplest definition of being paid to play, almost anyone can achieve that on some level by learning just cover songs or learning to read music. I play well enough to get paid. I could do it more if I spent more time practicing.
But as the talent level increases, the complexity of the nuances of both playing and composing increases.
I started as a drummer. Last night as I was driving home from a meeting, I was listening to some LZ on the radio. Sometimes I just listen to music as a whole, but I also listen to just one part of a song all the way through concentrating on, say, just the bass or keyboard or rhythm guitar.
Last night I listened carefully to John Bonham's drumming on
Nobody's Fault But Mine. The rhythms and syncopation are just absolutely unreal! If I practice hard, I'll be able to play it note for note, and on a single bass. But could I have
composed that drum part? I have serious self doubts.
