Arsenals form is better than forests but that doesn't mean that their form is sound, compared to the previous season I think that they are a little slow now. This game is a tough one and your verdict isn't far from what I had in mind. Nottingham wouldn't want to give up easily so it would be a defensive game on their part which can lead to a draw but the chances of arsenal winning this game is quite high to me
Arsenal appears to be slower than in their previous season due to how Arteta forces them to play and considering how Nottingham Forest's new manager
[Ange] sets up his team, I have a feeling they'll try to hold a high line, so it'd be an interesting game
[having said that, there's a lot of changes with their team, so I expect Arsenal to win it easily].
At the same time, Manchester city's defense is also weak. We have seen city's weak defense against brighton and tottenham. We should not expect too much from city this season. We also have to be very careful when betting on city's matches. Manchester City will play against Manchester united in the next match. I do not dare to bet on City's victory in this match either. There is a big possibility of City losing points.
You have a point about City's weak defense, but if Donnarumma plays on Sunday, I expect him to make lots of saves, so I'd go with a draw.