Their defenses stats tend to suggest better than just solid (I had them for fantasy, I know)
They forced an absolutely ridiculous amount of turnovers (mostly picks) and that's the thing that got them past the vikes in to win the conference champ and won them the super bowl against the colts; they didn't win those games by scoring 30 more points than the colts or Vikings;
they weren't scoring like 5-6 TDs on offense their big games, they had a really good defense that got 26 INTs on the season and led the league in TDs off of INTs and dominated in yards off of INTs and led the league in fumble return TDs; their offense was solid, yes. But what made them great was the way they were absolutely able to wreak havoc with turnovers and either get points off of them or get constant great set ups for their offense to score
their defense was not shut down; but the way it insanely forced turnovers and scores consistantly, made it great