Seattle has a great secondary. You need one or the other but without competent linebackers you leave the run open and open the passing game that way. We lack on the line and the secondary which is why our defense has struggled, though we have got better recently.
Back in 2005, the Giants had a dominant defensive line and a good secondary, but by the time they made the playoffs their starting linebackers were hit pretty hard by injuries.
They lost their first game in the playoffs by a score of 23-0...to the Panthers.