Maybe Green sucks, we sure don't have a confidence inspiring history with mid round OLs, but if we just got Doug Free's successor, I have no problems at all with that pick. Future starter.
You don't draft for immediate need. You draft so you have players in your pipeline when Free gets old, that way you don't have a situation where you are forcing Rob Petitti into a starting role.
Taking a starting OT prospect in the third round 2-3 years before actually needing that player to start is both excellent thinking ahead as well as impressive commitment to ensuring the OL remains a dominant unit. Which is certainly more paramount than taking a fringe RB or maybe a guy with knee problems. Not only that but swing tackle is a important game day need as well so he saves a big veteran contract there and does actually fill an immediate need that otherwise would have had to be addressed with a veteran.
Again, my biggest complaint is that I liked other tackles better. I don't know much about Green -- maybe he's a whiff. But I don't blame the process of taking your future OT over a marginal RB, not in the slightest.