I have no problem upgrading on the o line but don't think you have to waste your highest picks on guards for example. For example San Francisco which has the best offensive line running the ball according to Football Outsiders had a 5th rounder for a center, Goodwin. Alex Boone who starts at right tackle is an undrafted free agent.
The best line protecting the quarterback, Detroit, has a guard in Robert Sims drafted by Seattle in the 5th round. Peterman on the other side was picked in the third round.
Lets look at NE who everyone toutes as having a great line. They have the philosophy of the next man up after injuries have caused issues. Still when their right tackle went down, Volmer- a second rounder, Marcus Cannon stepped in who is a fifth rounder with good results. Dan Connolly, their starting right guard is an undrafted free agent.
Let me check the moon lately, maybe it is a tad bit blue..........................................
Well, it doesn't mean all the starting linemans should be first rounders. But you cannot get away with all of them being undrafted FA. Just like any team the best 2 or 3 players are normally first rounders with other supporting cast. When you have a big time talent on your teams he carries the load for the supporting cast. Some tacles are so good that in certain plays they can block 2 players at once. If you have two players like on your offensive line the supporting cast can get away with making mistakes. Remember, those O lines are going against first round talents like Watt, Von Miller, etc. every sunday.
Also, there is a difference between being a back up player and being the 'guy'. Back ups always come in games and do well until they're named the starter with bigger money and more expections then they crumble and get other players injured. When backups come in the game they're playing with house money.