They assumed it because Al-Nassr won Saudi Professional League only one season before appearance of Cristiano Ronaldo in their club. They bought more star players, not only Cristiano Ronaldo and in assumption, their strength must become stronger and their squad must be more competitive. Unfortunately, Saudi Professional League have Al-Ittihad, that won Saudi Professional League in a first season of C. Ronaldo for Al-Nassr. Then Al-Hilal, a most successful club in Saudi Professional League returned to their winning track and became a biggest barrier for Al-Nassr in two latest seasons.
Al Nassr won SPL trophy in the season 2018-2019. It was quite far from the time when Ronaldo joined the team. After that season, Al Hilal dominated SPL and won many trophies. In 2023, Al Nassr bought some players, including Ronaldo. But Al Hilal also bought many players, including Mitrovic. So, actually the top teams in SPL also did the same way as Al Nassr. But people too focused on Ronaldo because of the big name of Ronaldo.
He has a crucial role in Al-Nassr and I think he did it well for them. As a club, a team, they must know that dependence on a very old player like Cristiano Ronaldo is not good strategy and it won't help them to win Saudi Professional League. They must see their weakness in defense, improve it so that they can win Saudi Professional League. If defense weakness won't be fixed, they will continue losing points to weak teams in Saudi Professional League and fail in a title competition.
Ronaldo has contributed much for Al Nassr. He has scored many goals and made Al Nassr attacking be sharper. But Al Nassr board didn't really improve the defense line. I think Al Nassr board must focus on the defense line now, they need to rebuild the defense line to win the SPL trophy again.