So does Google demote it because of the broken external links at the bottom of the page, even though it should be number 1 based on its content?
Final ranking depends upon many factors. But here is your answer:
Yes, the ranking score will decrease because -
1. broken external links:- a. Most probably there was a back link from some of these external links b. The page refer to a broken link has a bad content (broken link)
2. no update in last 9 years. a. content freshness - a good quality content loose it's quality score if not updated for long time. b. competitive content quality - other sites may have generated better content in last 9 years.