Looking at the team, for me, it's the biggest question mark position group we have. It just seems, there are year's where we have 2 or 3 (or more, sadly) position groups that aren't championship caliber. That's not typically the OL. We usually field a solid unit there.
The Quinn years and Clausen years had great QB play, receiver play, TE play, OL play for the most part, but to be matched with an atrocious defense. More recently, in particular the Book year's and the past few years, it's felt like we've been a quality QB away from winning. The past few years, WR play has been horrible.
We may still be a deep playoff contending team, but the offense will struggle if we can't block anyone. I'm hoping they come of age quickly.