I'll agree that Dilfer is one of the worst QB's to win a Super Bowl, but that team beat the previous two teams and the team two years later that represented the AFC. They had Jamal Lewis and Priest Holmes as one of the best one-two punches in the modern era with Johnathon Ogden blocking and Shannon Sharpe to help resemble some passing attack. That D was so nasty that they had four shutouts, only allow 20 points three times, and more than 23 once. Lewis, Woodson, Siragusa, Sam Adams, Jamie Sharper, Michael McCrary, Chris McAlister, Duane Starks, and Peter Boulware were all well respected players at their positions, amassing 37 pro bowls amongst them careers.
IMO, the worst team to win is the 2005 Steelers where they needed the officials to rig the game in their favor. They benefitted from the worst one sided officiating that I have ever seen in a game where I was remaining neutral.