Most of the fans knew that the defense would lose a playoff game. If the fans knew it, the coaches should have known it.
The Cowboys formula was to win with offense and be just good enough on defense.
The Cowboys offense didn't achieve that plan in the 1st half. They were playing a limited Packers defense but struggled in the 1st half. Penalties were a big part of the reason the offense struggled, but since they didn't score points, they had to get away from the running game which had been a big part of limiting the exposure of the Cowboys defense during the season.
I'm not saying the defense was good by any means, but the Cowboys had a formula during the season that worked and the offense was a big part of the reason that formula didn't work in the playoff game.
On defense, bend-but-don't-break was a big part of the overall formula that resulted in 13 regular season wins. They couldn't just abruptly change the formula for the playoffs.
When the Cowboys beat Green Bay during the season, the media gave much of the credit to containing Rodgers to Marinelli's decision to play extra players in coverage with less pass rushers on many snaps. During the week 16 blowout win over the Lions, Jon Gruden went on and on about how Marinelli's 3-2-6 defense was they key to that game and had been a big part of previous games. That defensive formation is about putting more players in coverage with (in theory) a weaker pass rush.
It would be exciting to have a more aggressive defensive approach, but we saw with Rob Ryan that being aggressive and having a "modern" approach to defense could backfire in big way.
What the Cowboys defense really needs is more talent. They need an elite pass rusher. If they can't get that, then upgrading the coverage players would allow the defense to take more chances to generate a pass rush.