As I recall "On Writing" does not have a great deal to say about writing, it's much more about the life of a writer. To get a pretty good book that is actually about writing you'd want to upgrade to William Zinsser's "On Writing Well." So...

I read the first two sections of On Writing and that was enough for me. The first is a memoir from Stephen King in which he goes through major events in his life. The second is a writing style guide which centers around one theme: simplicity in writing allows for greater imagination in the reader. The second section goes through sentence structure, syntax, verb/adverb choice, pronoun placement, ect.

I would agree that the first section does not say a great deal about writing, but the second section reminded me of sitting in my High School english class with my favorite teacher writing a couple sentences on the board as an example and passionately (oops) dissecting the structure with arrows and margin notes to explain how and why a certain picture was playing in my mind while reading them.

Placing King's personal anecdotes and thoughts about the "life of a writer" before the actual lesson felt to me, when I began the second section, like I was sitting in the classroom of an artist who has far more passion for his work than I have ever felt for anything in my life before then. It made the writing lesson more impactful, if anything.

But it certainly had a lot to say about writing.

The document itself is titled "Essays on CIA Writing". And, it's largely on trends observed within CIA writing, so I'd argue that it's well titled.

Or, complying with the CIA's guidelines regarding capitalization:

"On writing".

Well once you've distilled it down that far, might as well drop 'On' because it's not adding much.

"Writing."

Agreed.

Isn't the "on" implicit if the title were just "Writing".

If the book was just writing and not concerning the subject it would be "writings" so there should be no confusion?

This is quickly turning into a new comic idea for Randall Munroe (XKCD)

Writing That Works