Well don't stop at sixth-round picks, why not talk about undrafted free agents? Justin Tucker, Bart Scott, Mike Flynn, Priest Holmes, Dannell Ellerbe, Ma'ake Kemoeatu,etc, I'd like to see a team with a better record than that on players that in an earlier era would have been 8th or 9th-round draft picks. There isn't one. Historically you have a 4% chance of finding a Pro Bowl player in the sixth-round. You have a less than 1% chance of finding one in the seventh-round. Now a player doesn't have to make the Pro Bowl to be a quality player but when people talk about teams drafting in the late rounds, they're talking about a lottery pick.
Last year NFL.com did a story on the best late-round picks of the last 5-years and there were some great players--Antonio Brown, Kelvin Beachum, Greg Hardy and Jason Kelce are the best of the bunch, the other players they featured, 8 others, were situational guys or quality starters like Alfred Morris. When you use an AV scale as the ESPN article does, the scale becomes skewed if you're lucky enough to get one of those lottery picks because so few late-round picks amount to anything across the league, one gem will weight the scale disproportionately. Look at the list of teams that allegedly draft well in the late rounds--lots of perennial doormats higher on the list.
The ESPN article defines value in the late-rounds between 4-7 as opposed to just the last 2 rounds and if you want to go back the last 20-years the Ravens have a great deal of success in that range: Jeff Mitchell, Adalius Thomas (6th round), Chester Taylor, Tony Pashos, Jarrett Johnson, Derek Anderson, Sam Koch, La'Ron McClain, Dennis Pitta, Tyrod Taylor, Darnell McPhee, Ricky Wagner. 4 of these players made at least 1 Pro Bowl and Adalius Thomas and McClain were first-team All-Pro. The moral of the story is don't judge a front office by its inability to get a Richard Sherman, Tom Brady or Antonio Brown in the sixth-round because they are historically rare, with emphasis on "historically!", only one sixth-rounder has ever made the Hall of Fame--Jack Christiansen, drafted 2 decades before the merger when there were only 12 teams.