How about the Steelers are a better team?
San Diego under-performs consistently, and Norv and Marty before him are known for that, aren't they?
They win plenty, but when they face good teams they always come up short. A lot of it is the players themselves, but it comes back to the coach who decides who to put on the field. Some players get it done consistently and the coaches recognize that and put them in, and if they don't have them, they go out and get players who can get it done.
The Steelers are a real good football team in spite of the early season performance. The Chargers are also a good team, but not quite as good.
The coach has a lot to do with that. You can't spot a team 14 points and expect to come back. The Steelers came out and took control of the game right away, that's how to play football. It takes away the other team's running game and it screws up ball control and time of possession. It's almost impossible to come back from a deficit like that no matter how good your team is.
Inevitably you run out of energy and make mistakes like failing to convert on a critical third down. The other team's defense is all over you because they're still fresh.
The bad thing about it is that San Diego could be the winning team, but losses like this one kill their confidence. Now, when they get into this situation again, they'll be thinking "here we go again". It takes a lot to reverse that mentality, and I don't think Norv is the coach to do it.