That isn't necessarily a fair way to compare things by using the minutes. I would agree that the depth is a factor because we lose a 2nd/3rd line center in Rossi and so the center depth is lowered one notch. Ohgren is not a top 20 player for this club at the moment and is in there due to a pretty deep list of injuries. Yes, I guess that too does impact depth but a team also can't have contender mentality and strength with as many injuries as currently piled up for the Wild now.
Your assessment also doesn't consider that Faber now finally has a guy he can skate with and keep up. That top line D can now skate 24-28 minutes a game as they both have the stamina and strength to do so. That may not be the case every night right now in the middle of the season but in big games and in the playoffs, they will get 28 minutes and that will matter covering any lack of depth you speak of to some extent.