You really throw out the main point on what is keeping Al-Nassr down from lifting the Saudi League trophy, even when they have Ronaldo in their squad.
Someone who knows Ronaldo would tell you the kind of input Ronaldo puts into any team he plays for. He likes teamwork, and he doesn't feel happy if, after all his efforts, they lose their match because of weak defense or if the team is not playing as a team. That alone pains him a lot.
I have watched Ronaldo play in Al-Nassr matches. He always feels pain whenever they lose, and the cause of their loss is their weak defense. If that can be fixed, Al-Nassr can hopefully win the Saudi Professional League trophy
They began a season well, with a big and scored 5 goals while did not have any conceded goal which is surely very good start for them. With high quality and competitiveness of Al Ittihad and Al-Hilal as well as rising Al-Ahli and general improvements from those clubs' player resources, Al-Nassr will have to beat many competitors in Saudi Professional League to lift the trophy.
It won't be an easy season for Al-Nassr, and it potentially is more difficult than three latest seasons so Al-Nassr must become much better to be a champion in this season. They have a good start but it's not enough and they must maintain good performances and gain as most points as possible in coming matches.