If you are a team manager and you do not have many quality players in your team to make team rotation easy, as you team plays more games and you keep using the same players, they will be exhausted, and their performance will drop which will affect the team's performance, that looks like Arsenal's problem last season, not that the manager has poor managerial skill.
I think this incident will be a very valuable experience for Arteta. What happened to Arsenal is normal because the manager has wasted a lot of time but they haven't prepared good players on the bench. It was clear that in the end they tipped the balance in the game towards the end of the Premier League as all the regular players were slowly losing form due to the amount of games they had been in. I think it's normal that most people, including Arsenal fans, blame the manager for this, because after all he controls all the strategy in every game. Next season will be the most prestigious event in the Premier League, because it is clear that all clubs including Arsenal will provide significant competition to other clubs trying to block it and Arteta will not give Manchester City a chance to win another title which failed last season.