Koppen might not be as versatile as some of the other linemen himself, but his presence gives the team as a whole more offensive line versatility, as it frees them up to move Connolly to where they need him most.
If Waters doesn't come back, I think Solder, Mankins, Koppen, Connolly and Volmer is the best starting o-line. I think the drop-off from Connolly at RG to any of the other 2nd/3rd string OGs is steeper than drop-off from Connolly to Koppen at center.
If Waters does come back, than Koppen goes to the bench and Connolly moves to center, and if there's an injury to either of the guards, having Koppen allows the team to move Connolly over to guard.
And of course, if Connolly himself gets hurt, Koppen's experience and familiarity with Brady makes him clearly a head-and-shoulders better option at center than any of the other backup guards.