The Celtics completely overpowered the Lakers throughout the finals. Even if the finals were say a ten game series the Celtics still would have blown the Lakers out of the water.
Just look at the fashion that the Celtics beat them in Game Six. They beat them by 39 points. The last 4+ minutes of Game 6 none of the Celtics starters were on the court.
The Lakers were being toyed around with the entire series just like everyone else the Celtics played throughout the 2008 NBA Playoffs.
Just watching the last 4+ minutes of Game 6 you see how good the Celtics really are because they toyed around with the Lakers with their Bench players.