Arsenal are strengthening their squad ahead of the season. These new additions would require adjustment to a new league, and are here to replace aging or injured players who have enjoyed knowledge of the league.
While Manchester City don't have to change last season's squad much except for KDB and where injury forced them. They have time to integrate their new additions.
And also, why do you think that Arsenal will win the league if Manchester City had one of their fewest total points tally last season & Arsenal couldn't usurp them? I predicted Arsenal as second but again I wouldn't be surprised of Liverpool overtakes them as 2nd & there's ample evidence/logic to that.
I think Arteta will have to move differently this season, if he wants to win the league. Arteta needs to make decisions quicker. It takes him like 3-4 games before he arrests a situation.
Manchester City will have periods in the season where they will drop points, Arsenal should be capitalizing on every single slip up. That’s the only way.
Arsenal looks like they are making good changes there is no doubt about that, but it doesn't really look like it's enough because while they are getting new players, it takes time for those players to adjust to a new club and that could be an issue. Remember, these are all just regular humans, they might be making millions but they still need to go grab that candy they like, for cheat day, and may not have that in London, that is one thing to be upset about.
Now you may think, candy? Really? But, what I mean is that there are million things like that, candy is just the most obvious smallest tiniest example, there are million things you are changing. Only thing that would work would be transferring from Chelsea to arsenal lol, that seems like it doesn't change a thing.