Injuries kill any team, which is why I think using Super Bowl rings as the end-all be-all for determining a legacy is pretty silly. You could make the argument, sure, that Seattle would have won the game if both teams were totally healthy. By the same token, you could easily make an argument that the Pats might have won the other 2 SBs they lost with a healthy roster. Winning a Super Bowl and keeping enough healthy players to do so requires so much luck it's insane.
I will also say, however, that staying healthy and being durable is also part of what a player brings to the table. Just off the top of my head, the Pats gave up Talib basically only because he was injured for two postseasons when they needed him. Stuff like Bountygate obviously puts a different spin on that. But you have to admire someone like Edelmen, who gets smashed every game and never seems to get injured.