Center is the least important position on the line in terms on effect on offensive play. Might as well move him to LB. I'm being hyperbolic, of course.
Centers spend more time uncovered than guards and they'll often help with blocking but if you don't have a good guard the DT will blow right past and screw up the play. Sure, you want a smart guy at center if you can, someone with some movement skills to get lateral and help block or pull and of course hike the ball but guys can be taught that (mostly).
Look at the price of guards vs centers, look at where they're drafted vs centers. Now, a great center isn't anything to sneeze at but a great center vs a great guard, teams will pick the great guard every day and twice on Sunday.
We have a great guard. Why hurt the line by moving him to center?
