The Chargers are not overrated because, as AchrisK said, they have improved on their deficiencies. Their special teams has become much more sound and they've also proven that they can win with depth on both sides of the ball. I would be surprised if the Chargers were not the 3 seed in the AFC this year.
Regarding a potential rule change to disallow a losing team from advancing into the playoffs: I disagree with this. Teams play in divisions. Every team's number one priority is to win their division. If they don't win their own division then they have no scapegoat. Every team goes through periods of ineffectiveness, and sometimes it affects an entire conference at the same time. But the 49ers have won 5 super bowls. The Seahawks were in the super bowl 5 years ago. The Rams were in two super bowls a decade ago. The Cardinals are 2 seasons removed from a super bowl. Right now they're all teams looking for answers. But that has nothing to do with whether or not the division deserves to have a team in the playoffs. Besides, if they win a playoff game, then it proves that they deserved to be there. If they lose, then they're quickly eliminated and there's no discussion. And if you're not one of the two best teams to not win your division, then I don't have much sympathy for you. Division winners get rewarded with a playoff spot. That is the incentive for winning your division.
Now on to the Steelers...
I don't really have a ton of things to say this time. They got lucky in the end, but they only needed to get lucky because of their own errors. Yes, they almost lost to the Bills when Stevie Johnson dropped a 40 yard touchdown pass that was in his hands in the end zone in overtime, but the other team has to execute to win too. It's not Ike Taylor's fault he didn't do his job.
The Steelers looked great on the opening drive, possibly their most impressive opening drive of the season, which isn't saying much, but they couldn't maintain that momentum despite having possession for almost the entire first half, and they only led 13-0 at halftime because of failures to execute when it counted. On the plus side, new kick Shaun Suisham was 4 for 4 on the day with all of his FGs coming between 40 and 49 yards.
The running game was overall effective, but unimpressive against a bad rushing defense. This is on the offensive line and not on the running backs. Mendenhall had 151 yards, but he needed 36 carries to get them. Redman was very effective when given the opportunity. I believe he had 5 carries for 25 yards, many of them in 3rd and short situations. He still needs to be utilized more. Mewelde Moore has turned around from his very slow start at the beginning of the season, thankfully, but he's still nothing more than a change of pace back with the occasional hot route or dump off pass on 3rd down. I think this is his last year here.
There was really only one bad play on defense, and that was the touchdown, obviously. A 65 yard catch and run to a running back. By far the worst play allowed by this defense this year, but I guess even that is saying something about how they've played up to this point. Troy Polamalu had a great game and another timely interception to stall a Bills drive in the redzone late in the game. William Gay stepped up big when Bryant McFadden left with a hamstring injury. McFadden is questionable to play next week, which could be an issue. If he doesn't play, Keenan Lewis or Crezdon Butler need to step up. James Harrison also had another good game with a sack and a forced fumble and a $25,000 fine.
Brett Keisel should finally be back this week, which is just in time because Nick Eason just sprained his MCL, though Tomlin says he's optimistic about him playing as well. Having another D lineman in the rotation should help with the pass rush, especially with a starter returning, as Keisel is better at taking up blockers than Eason. Aaron Smith has for a while now been projected to return in week 16 against the Panthers and I haven't heard anything to the contrary regarding that thus far. I hope that he is back by then, giving him two games to get ready for the postseason. And of course, it wouldn't be a Steelers season without Roethlisberger battling an injury at some point, and it's finally happened. He has a sprained foot and is in a walking boot, but there's no way in hell he's not playing. He got injured in the second quarter and it was never even a question that he wouldn't finish the game. He even had an 18 yard scramble on a 3rd and 17, so it can't be too awful. His mobility will possibly suffer a bit, but maybe him being pressured more to stay in the pocket will be a good thing.
Mike Wallace and Emmanuel Sanders both had key drops during the game. Shit happens, but when it does, it still sucks. Sanders needs to keep his head up, and Tomlin needs to continue to allow him to improve. And of course Wallace is only a year in advance of Sanders in NFL age. They're both young guys with lots of room to improve.