I blame John Harbaugh for every Ravens loss to Pittsburgh, because every time he faces the Steelers he loses his shit.
I think Flacco is underrated for a couple reasons.
One, he is incredibly durable. He can take a beating and still be on the field, and I think that is a big reason for why the Ravens are a contender every season. They never have a 4-game stretch where they are playing Luke McCown at QB or something like that.
Two, I think he's been handcuffed by the Ravens offense to a certain degree. Flacco throws a great deep ball...he could be the best deep thrower in the NFL, but for most of his career he's been stuck with slow WRs like Boldin and Mason. His best deep threat was Todd Heap, because he could at least lob the ball to him. Torrey Smith has been good for Flacco this year, but I think that aspect of Flacco's game has been underutilized.