I think the big difference is the run game. Seattle's bread and butter has always been their defense, but that is buttressed by a smashmouth dominant run game. They used to have a fantastic run blocking OL and good RB's. Now they've traded away or let go via free agency some of their best OL. Now Marshawn Lynch retired ... and his spirit returned as Jay Ajayi.
We grinded away at Buffalo, keeping their offense off the field. We contained Tyrod and stuffed those run lanes. We ran the football down their throats, and didn't let their offense get a rhythm. Jordan Phillips out-physicaled Ritchie Incognito. As great as the Seattle defense is ... I'm not sure they were ready for a smashmouth OL. Our OL was still learning each other and the system, and doing so without everyone healthy when we played in Seattle. And ... we still almost beat them.
This is a surprising season. The AFC West is shockingly dominant at the top and every team is tough. The NFC East is surprisingly good top to bottom. And, so far, the AFC East is the 3rd best division in football. It's not that the Bills or Jets are bad ... it's just that the Miami Dolphins are getting better.