Cech cost us the game quite clearly.
But the conservatism in going with the packed midfield again shows that Wenger has not learnt anything. Only more injuries leading to him stumbling upon a working formation will change things. So there's some hope, I suppose, with all the certain upcoming injuries.
Even when we had worse personnel in defence, I always felt that the lack of organisation in midfield or stupid mistakes like the one from Oxlade (yet again) were the main reason for all the pressure. I think that showed again today and when your goalkeeper plays like a clown on his debut, you're fucked.
No Walcott or Alexis means no quick movement up front, no guile, no unpredictability and no goals. Ox is good, but he's not a forward and we need at least two of Alexis, Theo or Ox to play. You can get away with playing a lone Giroud in some games, but over the season, the lack of a direct, incisive outlet will ultimately cost you.
The difference Bellerin makes should be obvious by now too. Anyone thinking Debuchy is for some reason a better defender should remember that Bellerin had outstanding games against City, United, Liverpool and Chelsea last season. Having players like Bellerin, Coquelin, Ox, Sanchez and Theo gives the team so much more energy and a new dimension. It also dilutes the creative players' uses when they've got no players or spaces to play with and pass to.
We'll bounce back comfortably from this and comfortably finish in the top three, but unless there's some clear-cut changes in team selection, there won't be progress. A couple of signings would certainly help, but they won't help us to a title if they're handicapped too.
And bring back Szczesny. He's the most decisive keeper on set-pieces we've had. If Cech has a few more games like that, it will become a huge problem.