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.