Those are PFF rankings which are certainly not the end-all for statistical analysis for football. They are done with human eyes (and all of the biases that go with them) tracking and charting the game.
Talkiong to Falcons fans, him and Baker (the LT) both did not do nearly as well in 2012 as they had in previous years, a lot of that being attributed to the Panthers and the Bucs getting better than being dumpster fires. There were not many people bemoaning the loss of Clabo in Atlanta that there were when Winston was released here.
My rule of thumb for stats is if you have to break up the stats to show that he was good for part of a season or whatever, you are probably trying to hard to paint the player in a positive light. A couple years ago Clabo was a really good OT but that is not the case anymore and if you look back on NFL history there have been plenty of guys who were good for a couple years then fizzled out.
I am pretty sure this years O-line is not going to be as good as it was under the best years of the Kubiak regime, I don't think it'll be as bad as it was last year. The Pats have gotten away with having mediocre to outright bad O-lines and almost non-existent running games, but they have a first ballot HOF'er slingin the ball. We have the Amish Rifle, a recovering from injury Foster and a huge huge hole at RT. This is a decent signing because it at least puts another body on that particular hole, and if he's not completely finished then Clabo should beat out Newton. I don't think he's going to come in here and turn the offense around, and I really don't think he's going to be so much better at RT than what we already have that we will overlook any deficiencies in his game. At this point in his career, he's just a guy, and I think the market and his availability this late into the offseason probably agree with these views.
Sometimes reality is a stone cold *****.