Bill Callahan is a great coach, there is no denying that. Any coach that has taken his team to a Super Bowl is deserving of that distinction.
But, is he the right guy for an offensive line? Take a look at his history, as a player and coach.
He was a quarterback in college. Through his coaching career, Callahan has coached tight ends, offensive line, quarterbacks and special teams. He has been a head coach as well as an offensive coordinator. My point? He is not concentrated in one spot, he has done a lot of work with different positions.
Now take a look at DeGuglielmo. He was an offensive lineman, and a good one. He has spent his career coaching offensive linemen, aside from a period where worked with tackles and tight ends. He is a lifer with the offensive line.
He will be able to go into more depth with technique, and strategy, and what goes into a lineman’s head. Linemen can relate to coaches that have done what they do. They get excited to play for coaches like that, and will play to the best of their abilities.