I would never claim to know the inner workings of the Cowboys but I feel confident that Garrett wanted Callahan here as an OL coach and nothing more. I would say that the way things have turned out, Garrett was absolutely right. Callahan sucked at play calling and at being the offensive coordinator. Garrett wanted Linehan, got him and from my perspective, all that has transpired since, is arguably complete vindication for Garrett and his process. And in case you forgot, Garrett blew up the OL long before Callahan ever got here. Status quo in regards to the OL when Garrett took over was not acceptable to him. and I believe the players on the OL at the time didn't buy in and that's why they were let go. That's a big reason I bought into Garrett's "process". Seems to me like it's working.
You seriously giving Callahan all of the credit for the OL? Come on man!?