Something occurred to me today. If a YouTube video is flagged and one of the YT support monkeys checks it out, they mark it "OK". All flaggings after that are ignored, because it's already been staff-reviewed.
So the key is to flag widely, not deeply. Flagging just the "top views" videos may be less effective than flagging the newer, not-yet-viewed-as-much vids.
Just speculations.