I suppose losing two Super Bowls to inferior teams hurt him...we know the truth.
Not to pick on you, because I very often see that same line of reasoning from a lot of fans (and sadly, media members as well), whether it be about a team, player or coach - but there is a rather large flaw in that logic.
For example, based on that reasoning the Falcons and Packers both had a better season than the 49ers did last year since SF lost in the Super Bowl but those other two teams did not - in spite of the fact that the 49ers beat both of them in the playoffs.
The reason this logic breaks down is because not every team gets to the Super Bowl an equal number of times. It is like applying regular season logic (where all teams eventually play an equal number of games) to championship games (where all teams do
not play an equal number of games.
While a loss in the Super Bowl, World Series, Stanley Cup Finals, or NBA Finals may cause a larger sting for players and fans than losing earlier in the post season (or missing the playoffs entirely), there is no logical reason to count that loss as a negative against a team, player or coach when judging their career performance - unless you also apply an equal or greater negative against every team, player or coach that did not advance that far.
To take it one step further, the same logic would mean that teams that missed the playoffs (e.g., Steelers, Jets, Jaguars) all had a better season than the 11 teams (e.g., Pats, Seahawks, Broncos) that lost at some point in the playoffs.
Getting back to the Belichick example: should he be considered to be a better coach had he gone one and done in the playoffs following the 2007 and 2011 seasons?
Let's take Belichick out of the discussion; should Marv Levy be considered to be a better coach had he lost four consecutive AFC championship games, rather than winning those four games?
That simply makes no sense whatsoever.