No, it's not a guarantee.
Did you guys actually watch every Patriots playoff game? Or did you just look at the numbers?
For all of our good defenses... we still had individual playoff games here and there where they would be bad or okay at best, and Brady would have to be great or clutch to win.
They weren't shutting down every opponent and holding them to 3 points like that Rams super bowl.
Marino isn't doing a 28-3, Marino is coming back down from 14 points twice in the same game, Marino isn't coming back down 10 against Seattle, Marino isn't dropping 37 at Arrowhead.
Marino himself had a lot of playoff duds, even in games his defense played well, or where they give him a chance.