This year appears to be an anomaly if that is the case. As Southpaw said, the top four offenses are the only teams left.
What you really need to be is A) excellent on one side of the ball, and B) adequate or better on the other.
The Greatest teams of all time were excellent on both sides, for a year or two, but your general Super Bowl winners are great on one side.
The Rams defense seemed to be the best, to start the year, but has suffered with injuries, and their offense has fallen off a tick.
The Saints have a great offense along with a stout run defense, but can be passed against.
The Chiefs have the best offense, but like D'Antoni's Suns, more scores means more opponent opportunities as well, and a weaker statistical defense.
The Patriots are talented and balanced, but it all depends on Brady. Very journeymanlike roster without him.
Blah, blah.....any one of these teams could easily win.