If you look at pass defense rankings from the 2017 season you’ll notice that the Pittsburgh Steelers finished fifth overall in yards allowed per game and 10th overall in completion percentage allowed. Those numbers and rankings are useless, however, and are essentially antiquated thanks to more advanced stats such as DVOA. Those sorts of stats and rankings aside, how defenses ultimately can defend against deep passes often times makes a huge difference on a game by game basis.
Thanks to the play of the Steelers offense last season, the team was able to overcome their defense being unable to defend well against deep passes.