It wasn't long ago that he was putting in some really solid performances to be fair, especially in the FA Cup, but he was solid for Arteta generally prior to this season. He has his strong points. I think it's more outlandish to suggest he's rubbish at everything.
That being said, when he's not in top form he's awful. The fundamentals of his game, particularly on the ball, are just not good enough to stand up to poor form. I think this year he's felt his spot under pressure. Forget Partey, even Elneny has started ahead of him on a couple of occasions.
He's coming to a bit of a crossroads as well, he'll be close to 29 with just 2 years left on his deal next summer, I think it will suit both parties to part ways, he doesn't strike me as someone who wants to sit on the bench.