I've known only a couple of writers who claimed that their first drafts were their last. Supposedly, the words came as notes once did to Mozart's brain: each one perfect as it was. Or, if you will: the entire book or concert was already completed...and simply transcribed. Well, hats off to Wolfgang. But those writers were delusional if they really did believe their novels couldn't have used lots more work. A low form of genius may be a play when a writer is able to get it all down in sellable form, in one swoop. But none of those writers who boasted to me of their first draft ability produced a single novel that stood the test of time.
And why be surprised about that? Consider how much is at play even we're working from a detailed outline:
1) Our brains are processing matters of plot, structure, pacing, character, grammar, word choice, style.
2) Our brains are also timing the release of vital info, especially in mysteries: clues that can't be delayed for too long but mustn't be revealed too quickly.
3) A daily tug of war goes between the left and right sides of our brains: the right side wants control, of course, but the left side wants us to throw in everything including the kitchen sink--so we can see what works out. If we have no control, we'll end up with a 1000 page novel we need to edit down to 300-400 pages. If we have too much control, we'll end up with a novel that has no real soul.
4) In the exhausting marathon of writing a long novel, we need to maintain our energy and keep our juices flowing. The psychology of composition becomes as important as the creative act.
Some will turn out first drafts that are cleaner and more polished. But none of should feel discouraged. Worlds are in collision, within us, when we get those first words down.