They already did. They bought Nathan Ake from Bournemouth this transfer window and he is a great defensive player, not that great but will definitely work well along with City squad. They have brought in Sane replacement as well. I think City are a great squad, they have players , coach and everything but they sometimes feel like get overconfident a lot and some underdogs take advantage of that.
Btw I am Gunners fan @Trofo. Last season didn't went well for the Gunners but I have slight hope for a better finish from Arsenal. Not expecting big like winning the PL but yeah Arteta is doing great and he will certainly change things in upcoming season. Second club I support is City.