There is no doubt that Arsenal team has improved very much, where there is doubt is if Arsenal can continue at the top till the end of the season. The road is still very long for Arsenal. And the only big team that Arsenal has faced is Manchester United and they trashed Arsenal. This means that Arsenal will find it difficult winning big teams.
Arsenal does not also have the type of team depth that Manchester City has. It can mean that Arsenal will have to choose to focus on Europa or the Epl. They may not be able to chase the both especially if one of the fine players has injury.
As far as I know this isn't the first time Arsenal have done it , few seasons ago they did the same but after the middle of the season they lost all power even though they are still playing with the same squad let's see if Arsenal repeat it again.