The Cowboys are one of only three teams that held their opponents to less than 20 points ten times. They are one of only two teams that held their opponents to 10 points or less six times.
It is the defenses that are inspired by the homefield advantage.
This defense pressures the quarterback constantly, creating mistakes and turnovers.
However, if the offense cannot get things going and stalls out to where the defense is spending too much time on the field, they will grow fatigued and falter.
The offense must be productive and should against this Packer defense. However, with the health of the offensive line you have the possibility of undrafted free agents playing significantly in a playoff game. This is much different than playing against a D-line that is just waiting for the season to end. A playoff defense will be performing at it's highest level and it's difficult to imagine a young, inexperienced backup matching that intensity.
There is also the significance of the running game in the playoffs. You definitely want to control the clock and a reliable running game plays an important role. The Cowboy's running attack is almost a novelty. There is very little power running and that might cost the Cowboys in a close playoff game.
One dimensional offenses rarely get oiut of the divisional round.