I doubt we'd have stayed in the top 4 had we stayed at Highbury. The fact that the billionaires rolled in ans bought up trophies left, right and centre just at the time when the stadium move did somewhat hamper us is not Wenger's fault. That said, we should have some trophies in that era. Now we have the money to compete there were some promising signs but Wenger has failed to push us on and for that he should be sacked. But he'll leave us with a squad which should be able to compete with a few additions and enough money to allow us to stay competitive.
Things could have gone better but they could certainly have gone a lot worse.