I would say Guardiola's brilliant match strategy is why Manchester City won the Premier League and Champions League titles. There is no doubt that Haaland is a very important player in City's squad. But it would be wrong to think that City won the title only because of Haaland. Manchester City's squad is very stable. And Manchester City is strong as a team. They weren't solely dependent on Haaland's performance. Guardiola changes his match strategy before various important matches. This is why City's performance was consistent throughout the season.
Indeed strategy is an important part in every game but not all players can apply the strategy correctly here I think Haaland can apply it well and find a great partner like Kevin De Bruyne ready to supply the ball. I don't deny that the Manchester City squad is stable and complete but Arsenal's squad is also not much different the weakness is in the second tier players , for this season as Arsenal have prepared it certainly do not want to repeat the same problem.
I think Arsenal's main problem last season was their weak bench team. And so if any player is injured then they cannot make a suitable replacement. And because of this, there was a gap in the team. Arsenal's performances lost consistency due to injuries to several players. Their performance is stable. And the group never got back to the truck. On the other hand, Manchester City's attacking players do not have to face many problems even if they get injured. They had talented players like Alvarez and Foden as backups.
Comparing Arsenal with Man City will not yield a good balance because the two are not the same when it comes to the brilliance and consistency of their coaches. The weakness in Arsenal later got revealed due to a few injuries and all these still lead to the blame of the coach as that is part of what is expected of him to get the viable mains and backups. You also have a good observation that Alvarez and Foden are good backups for Man City, it is part of the plan. Even at that, Arsenal got relented months to the end of last season, they can't simply get it done with such unwilling morale shown.