Flacco is a 2nd tier QB. His flaw can be fatal in that he's horrible at sliding protections, audibles, and hot reads. The teams that can generate pressure while mixing up their defensive schemes eat him alive.
And I don't want to hear the general statement that any QB would have struggled today. No, Manning, Brady, Rodgers, and other guys who can make good presnap decisions would be figuring out what Hou was doing and changing things up at the LOS. Hell, Andy Dalton would have figured out some of those D playcalls and audibled to some quick screens and eaten up chunks of yards.
You must not watch a lot of football. Just last week, Rodgers shit the bed against the Bills. This is pretty standard for QBs, they have bad games from time to time. That's ignoring a lot of other team factors that led to the loss again today, but then again the lack of exposure must keep you from seeing things like that.