Having begun “The Master of Ballantrae”

My pen is clear enough to tell a plain tale; but to render the effect of an infinity of small things, not one great enough in itself to be narrated; and to translate the story of looks, and the message of voices when they are saying no great matter; and to put in half a page the essence of near eighteen months – this is what I despair to accomplish.
Robert Louis Stevenson: The Master of Ballantrae, Chapter II.
It seems to me Stevenson excuses himself because his novels are not so heavy as those by Walter Scott and Charles Dickens. But I wonder if that makes them “plain”?