Flacco had good playoff runs the year before that. He outplayed Tom Brady the year before but his kicker missed a chip shot so they loss the game. He's outplayed Roethlisberger in the playoffs too but TJ dropped that TD pass that hit him right on the hands.
As for the Broncos game. Peyton Manning only put up two touchdowns against that Legendary Ravens defense. the special teams spotted Peyton two touchdowns. you can always cherry pick a play, but Flacco wouldn't have thrown that pass if Jacoby wasn't that open. He was playing the game incredibly well and still had 37 to 40 seconds to score a TD and tie the game. That TD didn't end the game it only tied it. Than the Ravens won it in overtime after Peyton though that pick.
People usually misinterpret that game but the Ravens out played them on offense and defense. The Broncos outplayed the Ravens on special teams.
Again I strongly believe that QBs get too much credit and too much blame same goes to the greats like Brady and Brees, but Flacco is historically one of the most clutch post season Abs. After his first two years he always plays incredibly well in the playoffs and championship games his QBR usually goes up over 20 points.