Nonetheless, Mickey Spillane was the author of scores (hundreds?) of novels. As a writer, he wrote them. He was their author. We just don't ordinarily express it as, "Spillane was the writer of countless popular novels." No, notwithstanding that the statement is true. It is simply not correct (that is, generally accepted and preferred) idiomatic usage. The word there is "author." But he wrote them--he did not "author" them. (No one, I think, would quibble with "Spillane wrote countless popular novels.")
Where matters become more difficult is the self-description as "author" vs. "writer." And that gets back to status vs. occupation. Which does the speaker wish to emphasize, status or occupation?
But there is no clear line. Consider T. E. (Tom) Watson, whose business cards describe him as "Children's Author T. E. Watson." Yes, he writes the books (a lot of them, legitimately published), and makes a living from his books and related activities. But somehow, "Children's Writer" does not sound right, and he wishes to allude to the fact that many of his books have been published and that is his profession (personal appearances as author being part of the whole picture). On the other hand, I know some folks who put "Author" on their business cards while either being aspiring (unpublished) writers or having a very limited (micro-press, one or two books) record. The word there seems pretentious, or at least premature.
My views, FWIW.
--Ken