You are so valid, current performance is not indicative of future performance, Man City did well this season but that doesn't mean that they did not have changes. And if Arsenal could have done better than relenting when they needed to fight most, they would have won the title. Next season is another chapter that no one knows yet, there are viable contenders in the line-up.
That's right, Manchester City won the Premier League title last season, they even became a club that won the Treble Winner. But indeed, even though they have everything today, it is not certain that next season they will be able to do it again or be able to win the same title. All clubs make a lot of improvements for the Premier League next season, including Arsenal. No one knows who will win the Premier League title next season because it is quite difficult to predict, for sure I know for sure that Arteta will not waste the opportunity to win the title next season after his failure last season.