I know Baas is not well loved, but I don't think he's as big a problem as we think. I am with you +10 on a RT at #1 or 2 and even a RG later in the draft. I see the OLine as a unit more than any other group of players on the team. When you have a weak ling (Diehl) it adversely affects the rest of the line on that side of the ball. So Lane Johnson would be a great pick up for us.
To be honest, while LT is a very important position in its own right, from what I've heard nowadays, the most important position on the line is actually the C. Not for physical athletic ability (that is still the tackles that need the most beef), but for intelligence. A good Center can coordinate well with his QB to call out protection schemes and identify blitzers, tweak blocking schemes on runs based on what the defense presents, etc.