I am no analyst but what I saw was:
Rivers didn't make any mistakes. He took what the D was giving and his playmakers turned those small plays into big plays. D line couldn't get to Rivers. Certain CB's that can't cover or tackle. I think the comparison to Wanstants D is reasonable.
SD was not afraid of the Bills offense at all by the end of the game. They got conservative otherwise they probably could have hung more points on them.
Overall the got beat up front on both sides of the ball.