Let's put things into perspective here folks...
No team in the history of the NFL has ever won a championship simply by having a great QB. They win because they have a great defense, a consistent running game, solid special teams, and a good QB.
We have all seen some of the greatest QBs ever to play NOT win championships because their defense let them down or they didn't have a running game to support them (Tittle, Jurgensen, Fouts, Moon, Marino, etc.).
We have also seen some teams with not so great QBs win championships because they had outstanding defenses and running games ('91 Commanders, '00 Ravens for instance). Usually, it requires a complete team in order to win but sometimes if a couple of areas are strong enough you can compensate for the weaker areas.
When we won 3 SBs in the 90s we had a great QB in Aikman, the all-time leading rusher in Emmitt, and a very solid defense. Our STs were also excellent year in and year out.
My point in all this is that we have a great QB in Romo but we lack in those other areas at key points in the games. Our defense breaks down, our STs give up big returns late in games, our running game disappears, etc.
Those of us old enough to have watched Roger Staubach play can remember how many times he threw multiple INTs in a game only to lead us to victory in the end but it usually required that our defense also stepped up and made big plays late in those games. Larry Cole stuffing John Riggins for a loss or recovering a fumble (Cole was the man!). It wasn't simply Staubach playing great, which he did, it was the whole team's stepping up and that's what we are NOT seeing with this current team.
Romo made a great comeback the other night, TWICE!, but the defense failed to make stops on plays they were expecting.
Staubach, Montana and Elway are known for their late game comebacks but those usually had to happen because THEY made a bunch of mistakes early on. In the 1981 NFC Championship game (you know, "The Catch") we had dominated the game and Montana had thrown 3 INTs before leading his team down the field for the go ahead score. Wait, Saint Joe threw 3 INTs in that game? Yep, he sure did. But he gets a pass because they won. They wouldn't have won if not for Carlton Williamson making a fingertip tackle on Drew Pearson after the Clark TD. Pearson would have scored or at least put us in easy FG range and we would have won the game. If the blitz on Danny White hadn't caused him to fumble the ball we still had a chance to win it and Montana would have been labeled as the goat for throwing the game away.
I could go on and on (too late) but you get the idea. Great QBs make mistakes but they also find a way to come back from them. Romo has shown over and over that he has that ability. What is lacking is for the rest of the team to step up in those situations and make big plays like they did for Staubach, Montana, & Elway.