Lack of leaders and his arrogant tactics, or lack thereof, are the biggest downfalls IMO. I struggle to remember a strong Arsenal captain in the post Viera era. Henry and Fabregas were not real leaders, just the best player in the team. Gilberto Silva maybe to a small extent. As far as his tactics, at least they used to come off in an attractive manner. There was a time you won fuck all, but looked good doing it. No longer.
I slightly disagree with player development. I feel he has done a good job of scouting young talent, particuarly from France, over the years and making them into solid prem players. Those you mentioned in your article are certainly examples of where he has gotten it wrong. Lest we forget Henry was a failed winger at Juve. Around the time you lot moved to the Emirates you were a bit of a football factory for City and Barca, which spoke to his ability to develop: Adebayor, Sagna, Clichy, Hleb, RvP, heck even Ashley Cole all owe him a big debt of gratitude.