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It wasn't just luck, as Manchester City were experiencing a decline in form at the same time. Al Hilal capitalized on the opportunity to defeat Manchester City. After defeating Manchester City, Al Hilal was considered the favorite, but they were defeated by Fluminense. It's safe to say that Al Hilal's performance wasn't strong enough to compete in the CWC.
In the Saudi Arabian League, I have no doubt that Al Hilal remains the favorite to win the SPL title, but in European competition, SPL clubs are still far behind.
It's perfectly normal for SPL teams to be unable to be more consistent when facing European teams, so their wins won't always be frequent due to the quality of their players and the strength of their squads that aren't always strong in the long run. But in terms of competition in the SPL, I think what you said is also true. Al Hilal will still be the favorite to win the SPL title if there isn't a tough challenge from some of the other teams there. However, for next season, I'd like to see another team besides Al Hilal become the title favorite to make the SPL competition more interesting to watch.