Arsenal have tried over and over when Manchester City was dominating the league about 3 years ago, if they couldn't win it nor any other trophies this season how are we sure that they'll do well in the next one, I would be tough now Liverpool is in the picture and if Manchester City regain their form the Arsenal should forget about winning it.
Arsenal will not be able to win the Premier League title if they do not strengthen their squad. Arsenal's starting XI is strong. But their bench team is not strong. If they want to win the Premier League title, they will have to continue their good performance throughout the season. And for this, they should keep talented replacement players in the squad along with the main squad. As a result, even if any player in the squad faces injury, the overall performance of the squad remains stable.
But Arsenal does not have any worthy replacements for the players in the squad. So in the last three seasons, we have seen players lose their trucks after injuries. So I would say that Arsenal definitely need to add talented players to the squad if they are interested in competing for the title.