 If they made script doctoring SOP for every moderate/big budget film, it wouldn't reflect negatively on any one screenwriter.
 For a thousand dollar painting, respect the individual integrity of the artist. For a 200 million dollar feature production, get a few more pairs of eyes on the thing.
 2 or 3 doctors at the end of prepro with enough time to make necessary extensive changes to even the storyline, and another couple of doctors on hand during production who specialize in changes on-the-fly.