The reality is that it goes further than just depth. The OL is a great example of not having 5 starter level players to fill out the lineup. Another byproduct of "making it happen", but I'm always reminded that kicking the can doesn't have a cost.
They have $12 million in cap space. Had the chose to, they could have signed many more Offensive Linemen. They chose not to. I think it was a mistake, but it had nothing to do with not having the money to do it. If anything they didn't do it because they didn't want to push money into the future.
In addition, I think they should have taken another pick at OL in a draft that was very deep on the OL.