One thing you can't take away from Wenger is his ability to get a lot out of players and nurture there talent. We've seen it countless times over the past two decades.
The real issue is that he's gone from nurturing talent like RVP, Fabregas and so forth to nurturing the likes of Ramsey and Chamberlain. There is a considerably difference in quality between what he used to nurture and what he is dealing with now.
I don't ever doubt that as a manager he can get the best out of players. He just doesn't sign the kind of players he used to and ultimately the limited talent that he's dealing with is abundantly obvious when their careers stall and the talent we thought they had never materialises.