I get that, but when we are discussing Manchester City, they should never depend on one or two injuries in a way that destroys the whole season if that happens. Yes it can happen and if Messi was to get injured back when he played for Barcelona, it literally meant that the game is going to be completely different. But they should still be able to compensate for these incidents on a level that the season is still not that much at risk. It does change the trajectory of a season, but it shouldn't to the extent that it is game over as soon as an important player misses a lot of games.
City also had injuries last season, when De Bruyne suffered a very serious injury and was out for half a season and they were left without Gundogan, who went to Barcelona, but all this did not affect City, they played very well and became champions again, despite the fact that Arsenal pursued them until the last round. But last season their attack played better, when Haaland could not score, Foden helped, and now it is more difficult for them even despite the return of Gundogan, or maybe he has not yet regained his form.
Yes this is a good example that Manchester City should still be able to perform without some key players. As I said they still have a bench and while no bench of any team can be as good as the most important players starting every game, it can still be good enough to keep the quality of the team at a level that retains their competitiveness for a whole season. They can easily afford to put people like Grealish on the bench. They were able to compensate for De Bruyne last season such that they were still able to claim the title in the end. Rodri is a huge loss for the team and yet that doesn't make them less of a favorite for the Premier League title.