I'm not really worried about the power rankings, I really look at individual and team matchups.
Both the Seahawks and the 49ers return most of their squads intact. With these squads last year, in two games, the 49ers averaged 13 points per game against us. The Seahawks averaged 24 ppg against the 49ers. Based on this, our defensive matchups favor us against their offense, while our offense has a much easier time moving the ball and scoring against their defense.
So now we look at how the teams have changed this year. Injuries and FA are the two things that change the team, and the Niners are hurting really badly at WR. They have no one that can win their matchups outside on us, so if we can stop the run, and keep Kaepernick in the pocket, we win easily.
On defense, they lost a very good safety, and replaced him with a rookie. Now, he might step up and play very well, but he hasn't proven it yet, and that really can't be factored into any sort of power rankings. Their CBs have problems sustaining coverage without a pass rush. This has been proven by more than just us.
On our end, Harvin's injury doesn't mean a whole lot, since we didn't have him when we played them last year. Conversely, when the Niners played Minnesota, Harvin was a matchup nightmare against them and had a very good game. When he does come back, he will add a lot to the overall matchup. We've replaced our 3 tech DT, but it remains to be seen whether that will be better than what we had last year, so the advantage can go to the Niners in that matchup.
When you break it down piece by piece, and also take the entirely of the matchup, we're looking good. Sure, they beat us early in the year, but our offense was completely different than it was later in the year. Kaepernick made them a more dynamic and vertical offense, but the results from last year still take that into account. They don't have the weapons to force diversity; they will have to rely on the run game and Kaepernick making some sort of play.
Taking the season as a whole, we need to improve on our road schedule and our divisional schedule. It's hard to repeat 8-0 seasons at home, so say we drop one game. We have to make that up somewhere, and our 3 divisional games on the road is the place to start. It's a two-fer: 3 of our 5 losses on the road were in division, and all of our divisional losses were on the road. If we matchup well enough to hang another loss on the Niners, hang another loss on the Cardinals, and possibly hang another loss on the Rams, we make up at least 2 games. Factor in 1 loss at home (I don't want to, but the law of averages takes effect here), and a tougher road schedule and we can still offset those with divisonal road wins and end up at 11 or 12 wins. I think even 11 wins takes this division with all the improvements.