The team's evaluation of their whole oline over the last few years is questionable at best. Do you have a source on the team that backs that statement up?
You're right that in the past the evaluation of offensive lineman has been putrid.
But things have improved. Look at Smith. Yeah, it's easy to that he should be good because he was a high round draft pick, but there are several early 1st round tackles out there who aren't playing to his level.
They nabbed Parnell off of the Saint's practice, and in limited time has shown some positive attributes at both left and right tackle.
The Frederick pick was almost universally mocked and at the moment he's a top-10 center.
Leary... undrafted because of the knee has done a "OK" job as a starting guard. I would think that there's room for improvement.
And even Bern, who has taken a beating by fans has played pretty well this year.
Whatever the change, the Cowboys are doing a much better job at evaluating offensive line talent.