You have to win the Super Bowl to be the best--except when you don't.
The 2007 Patriots were one of the best teams of all-time, no doubt about it, and easily the best of the Pats teams. I watched every game hoping they'd lose and they just kept winning, until it all paid off with 35 seconds left in the 4th.
One last thought: I think part of the reason the Pats decimated teams at the start of the season, but that they are mere mortals in the later part of the season (Expected Win-Loss in first 8 games: 6.97, Expected Win-Loss in last 8 games: 6.03) was that coaches caught on to their spread offense. So maybe they weren't that great, they just benefited from change in strategy that it took time to adjust to. When you regress the Pats points-scored on the number of the game, there is a significant downward trend of about 1 pt per game (t = -2.600.