You are right, of course, people do write for different reasons. And in previous years, if you wrote to get something out of your system, it was in a private journal or diary. If you were an amateur – someone who wrote on occasion, you submitted to publications, received payment, and generally kept quiet about it. If you were a journalist or a copywriter or an author, you didn’t spend your days telling everybody that. And you certainly didn’t attempt to teach everybody your skills.
I don’t think your classifications make much sense. For instance, you give include two different groups of people under your heading ‘purists.’ They contradict each other – the one writes for money and the other doesn’t care about money. In any event, someone who writes for a living, as I do, is hardly a purist.
I’ve certainly been a ghostwriter. Not much I haven’t done in the world of writing.
I disagree that there are millions of readers out there. Percentage wise, most people don’t read a book after they leave school or university – 95% in fact. They just don’t like reading.