It was a successful side because of his strengths and it wasn't more successful because Wenger has flaws. This is what people don't seem to recognise. Maybe this isn't what people think but it comes across like people think Wenger was this genius of a manager back in the day and is now a bumbling idiot ™. The fact is he revolutionised the English game with his fitness regime and his knowledge of the European game. For a while we were just better than everyone else. And yes, people do talk about the Graham defence and while that was a factor it wasn't the main one, and the Invincibles defence was entirely his own.
Now we're not better than everyone else. Other clubs have caught up and arguably overtaken us with the fitness methods and worldwide scouting network. The billionaires swept in and bought up titles right at a time when our funds were (relatively speaking) restricted. We've lost the edge Wenger initially gave us. He's done pretty well to keep us in the top 4 during the stadium move, now we've got the new financial deals we should be pushing on. The FA Cups bought him some time to do so but this year we really needed to challenge. We did for a while but now we've fallen away. But that doesn't mean that he's suddenly an idiot or that the last 10 years have been an unmitigated failure.