my experience: a first novel takes 3+ drafts (i.e. complete rewrites) to get decent. That's not a happy factoid. You WANT to be done earlier than that. ...I'm just telling you what I believe to be the cold hard truth.
Obviously as a work gets larger, the danger of the structure collapsing in on itself out of gravity / inability for one person to architect it well increases. That said, my two books are really just one 340,000 word (1,360 page) novel. Structure is solid, but took TONS of work.