Koscielny is 26 now, I don't think we can make the same excuses for him as we can make for Miquel for example. He's put in some good performances in an Arsenal shirt, granted, but even in games when he's playing well, he's always prone to commit an enormous cock-up that costs us a goal. Moreover, I don't think he's a particularly brave defender, who'll put his head where it hurts and really relish a physical fight. He's good at making interceptions and nicking the ball off the opposition, but you need more to be a good defender. The only reason Wenger signed him last season is because he's cheap, and this sort of player may be good enough if your ambition is simply UCL qualification every season (although this is debatable), but he's nowhere near good enough if we want to win trophies.
So, ultimately, we'll have this chasm between supporters and management. Wenger doesn't care about trophies anymore, and is only bothered about the financial benefits of UCL qualification, so he's happy to play Koscielny and ignore his mistakes, while the fans will continue to tear their hair out.