Seahawks lost because of Brady shredding their defense. They were lucky to have even been in the title game. A banged up Arizona team, playing a third string quarterback lead them in the NFC West until the last game of the year. Seattle HAS to have home field to beat the Packers, then they lucked out when they were outplayed except for the last 4 minutes of the game when Packers self-destructed. So no, they didn’t blow the game to the Patriots. They were lucky to even be playing them.
My sense of the football difference of a few pounds is that the ball feels minimally different. That difference would not make it easier for Brady to throw passes through a swinging tire hanging from a tree. That would have been skill at any pressure.