Take this with a grain of salt since it's their own website, but Youtube themselves say they wouldn't be able to let any content on their platform stay up even if it slightly resembled copyrighted content. Think the current Content ID system times 10.
Content ID almost definitely operates on a score model, which I'm sure would scare Google into changing their minimum required score to remove a video. It would result in more false positives, but you can almost see the headline in your head if they don't "Youtube has over 50000 videos that their own Content ID Algorithm detected, but they didn't take them down!"