You can argue that Arsenal were in decline (the results indicated that that was clearly true) without arguing that Wenger was leaving the club in a terrible state. It depends on how bad he was at managing the players and money available to him.
Not sure how anyone can suggest that Arsenal as a club weren't far ahead of where we were when he arrived. In fact, virtually every analysis of his performance - no matter how bad - started with 'let's not forget what he has done for this club but...'