This is just a terrible flawed way to make it seem like UDFA's are as likely to be, what we consider to be starters, as 1st rounders. And even by his own admission. Except he doesn't think it's flawed because of it, but it truely is.
He is right, starters are always getting hurt across the league. And who usually replaces those guys? Depth players. So he's looking at a guy like Michael Jerrell last season and saying he's as likely a starter as anyone drafted in the 1st round.
It's not flawed at all. There are 160 starting OL every week in the NFL. It's the largest sample size of any position group, so the percentages don't lie.
The stats show that 72% of starting linemen are not 1st rounders. For every Walter Jones and Charles Cross, there is a Germain Ifedi and a James Carpenter as well.
Assuming first round picks are going to be better than late-round pics is bias.
First round picks will get more chances than late-round picks because there is a greater commitment from the organization for them to succeed, but due to the technicality of OL play the guys with the best combine numbers aren't necessarily going to be the best OL.
Case in point: Jordan Mailata, PFF's top-ranked OL, was a 7th round pick.