Well, Underhill did an article on it about 2 months ago, which is why this ranking is meh.
On average, if you're using PFF grades, only a handful of teams have 3 guys on their oline with players rated 70 or above. Most team, have no more than two good olineman and the rest are below average. The Saints are one of I think 10 teams that only have 1 player with above 70, and that's McCoy.
So if the Rookie, or Penning, or Saldiveri or even Ruiz grades above 70 they'll be above average. It's not nearly as bad as it's being made to seem. Oline play is trash across the NFL.