The word "greatness" has a few different meanings in my book, especially when talking about football. In the case of this article, greatness doesn't only mean individual numbers; it also deals with versatility and teamwork.
The players on this list are great because of their contributions to their team. They might not be great all-around players, but they play a very pivotal role.
It's also important to note the players on this list might not have rushed for 1,000 yards, but instead paved the way for the running back to gain those yards. They might not have recorded 15 sacks, but they occupied blockers to allow the sack artist to create pressure.