Seattle was definitely a more complete team, but they absolutely should not have been a more complete team on a 43-8 level. These were two 13-3 teams, one of which had one of the greatest quarterbacks of all time. This game came down to execution, not skill level. Denver was PLENTY talented enough to win this game. Seattle wanted it more all night long while Denver had a pathetic dear in their headlights look from the start. The Broncos completely crapped their pants in all three phases of the game. Seattle gets all of the credit in the world for obviously making Denver scared, but Denver's effort and execution was quite frankly pathetic. The Colts beat the Seahawks. The Seahawks are obviously great, but this should not have been a 43-8 game under any circumstances.
And no one on the planet is ever going to say that Manning's career is worthless. Everyone agrees that he is a top 5 or 10 QB of all time, and most would probably say 5 at this point. But he simply hasn't quite executed at a level to be the very best. He has had two opportunities to win a second Super Bowl ring, but just didn't get the job done. Four years ago he threw a catastrophic pick six against the Saints. Tonight his offense put up just 8 points. Sure the Broncos entire team was hideous tonight, but he was pretty bad himself. Manning is a top 5 all time quarterback IMO, but he just hasn't done enough with his Super Bowl opportunities to be considered the best.
As far as this Seattle D is concerned, I think they are maybe the best of all time when you factor in how the current rules overwhelmingly favor the offensive side of the ball.