Both Koscielny and Cahill could (and probably should) have gone. Would have made the game less of a spectacle but all it confirmed for me is that Arsenal are still miles off a title challenge.
Chelsea will probably end up walking the league. Man City are the only team capable of stopping them and even then they've already blown one chance to make ground on them by not beating them at their place. They're too erratic away from home anyway.
And there's no way De Gea is the best goalkeeper in the Premier League, and given the team I support I should know a thing or two about bad goalkeepers!