The number of pro bowls isn't really valid data when rating offensive linemen, is it? OL are often anonymous, which makes me want to bet those most often voted into the pro bowl were on TV a lot. The best teams are on TV the most. What's to say a guard could be factually average as a player, but he's on an offense with a HOF QB, HOF RB, HOF WR, and the team is really good and on TV all the time - and that guy getting a Pro Bowl nod? Is it really that absurd?
I played OL, I'm quite stingy to compliment an OL unless he's doing his job well nearly every play. To accurately rate an OL, you need film study. As with voters of a great many other things in sports, the voting tends to be lazy. Okay, I'll pick the left tackle on the team with a 1800 yard rusher who won 13 games....then no one will criticize the choice - kind of thing.
We don't have stats of how OL grade out game to game, especially back into the 90s. So it's just reputation thing (ie - no data). Meh.