Total points is also dependent on the quality of opponent, though. New England's NFL-leading points defense doesn't look as impressive when compared to its last-ranked schedule of opponents.
The Cards' defense is closer than you might think. The pass defense was 27th in DVOA with Patrick Peterson AWOL for half the year and Robert Alford on IR for the entire year. The rush defense was a more respectable 12th. Get healthy in the secondary and put another candle on the birthday cake, and you might have a solid unit again next year.
While DVOA does attempt to adjust for level of competition, it will never be 100% accurate because even the bad teams in the NFL can compete with pretty much anyone on any given Sunday.
That being said the lowest ranked defense of the 4 in the regular season according to DVOA has been exceptionally good in the playoffs. Thus further suggesting the need for a good defense.
The Titans' defense has been dominant in the playoffs, the 49ers' defense dominated last week and the Chiefs defense had a rough start, but completely dominated once their offense came alive.
The Packers also have a good defense and were looking like it for a majority of last weeks game before Russell Wilson started pretty much willing his offense down the field in the 2nd half.