I can agree with you on those points, I know (and the team knows) it's not Flacco or Rivers they are going up against, and that will make a difference. I'm excited to see how they match up honestly.
Underestimating our offense is a bad thing though, while the defense has had to win games in bad weather, our offense has had to play in that same weather as well and win those games (sometimes in close finishes). The Steelers offense has been playing better in the playoffs than they have for almost any game this year, in the cold. They will have the same advantage of warm weather and fast turf as the Cardinals do.
Their offensive statistics were poor for the regular season, but keep in mind they played 5 games without Parker (and a couple where he was not 100%), Mendenhall put on IR in week 4, TE Heath Miller out for a few games, an OL that only had one starter on it from the previous year, and playing half of their season against top ranked defenses. They had to overcome a crapload of adversity this year and while the defense did it's part in keeping games close enough for the offense to pull off wins, they are playing at a different level right now. The Steelers offense against the Cards D will be a truly interesting matchup as well, though it is being overlooked by the media far too much.