Most everyone thought that the Seahawks defense would be worse this season. The team lost lots of talent in the offseason. Gone were Richard Sherman and Michael Bennett and Kam Chancellor. That is a lot for one team to lose.
And at times this year, the defense has struggled. Not that Seattle has done poorly against bad offenses, but the Rams (twice) and the Chargers were both able to run well against Seattle. Still, against bad teams Seattle has sometimes imposed its will.
Seattle has also had to overcome the loss of Pro Bowl free safety Earl Thomas.