Putting the author in as a character opens a can of worms about degrees of reality and interaction among them which I think The Dark Tower has an easier time with than many because of having form the very beginning a very strong in-universe force of destiny, such that the telling of the story is not on a different scale as a working out of said force from the actions of the characters. Which is not to say that destiny as a concept does not usually irk me greatly, but King gets away with it pretty much on sheer wordskill, the resolution to the King-as-character element is far and away my fabvourite bit of the last volume. [ I think that's reasonably spoiler-free. ]