The poor defensive effort could be overcome because Romo is a very productive QB who can put up big numbers but in the end it wasn't able to be overcome because he folds when it matters most in spotlighted games. Denver's defensive effort was worse than the Cowboys but they were able to overcome it with a great offensive performance and a huge mistake by Romo. Manning had a turnover but his didn't come deep in his own territory with the game on the line with only 2 minutes to play. Ill-timed mistakes in your own end of the field can't be overcome in the final minutes of a tight game.
Apparently your whole argument appears to be based around the "ill-timed mistakes" or mistakes at the worst time thing since you seem to be mentioning that in just about every one of your many posts in this thread. You are from the Skip Bayless tree of football knowledge (let that sink in for awhile).
Scenario 1: QB#1 throws an INT at the beginning of the game (NOT the worst possible time - right?) and his team goes down 0-7. They go back and forth from there on out and the final score is 49-56 the other team wins. So that guy must not be a choker right? After all, he didn't make his mistake at the worst time.
Scenario 2: QB#2 and his team are tied with another team 49-49 and has the ball with 2 minutes to go. He throws an INT and his team loses 49-56. Wow, he isn't clutch because of the timing of the INT. QB#1 sure is a more clutch QB. Wrong. Almost every QB makes an error or two every game. The good teams have other facets that got their QBs back and help him win the game.
There is NO difference in the TIMING of the mistake when the situation is that all it takes is for ONE mistake to cause you to lose. Every single player should be allowed one mistake a game, they are only human. Both games are lost in the scenarios above because of one mistake from the QB. Both result in a loss. I don't see how the timing affects the clutch factor.
And this is without throwing any excuses as to why the QB threw that INT (WR wrong route thrown, great defensive play, foot being stepped on lol, etc)