FWIW, all the truly exceptional writers I've ever known and worked with never read a single book or took a single course on songwriting, they just did what came naturally. The organic approach doesn't just work for food. ;-)
I agree to a certain extent, Roger, but even natural talent needs guidance. I'm not saying I'm naturally talented (or even talented at all), but I know that I'd still be writing 4 to 5 minute songs with changing tense, too many characters, poor use of hook, etc. if I hadn't received sound advice from my NSAI song evaluations.