Every club in the Saudi League has strengthened their teams in such a way that it is difficult to distinguish between the big teams and the smaller teams. Ronaldo and Nasser play for the club and some other star players have joined the Al Nasser club so we consider this club as a strong club but outside of that there are clubs like Al Hilal and Etihad who have been performing very well. No match for Al Nasser is easy, every match requires a lot of hard work and proper planning to win. One season Al Nasser is the champion, another season Al Ittihad is the champion and another season Al Hilal is the champion, so there is still competition in this league and that is definitely a good thing.
It's easy, in order to know which are the big teams and which are the smaller teams depend on how much money they have, if they have a lot money, they're big teams and they able to sign European players. There's a competition in this league, but a competition among B class teams. 
If there's an A class team joined the league, they can easily win the league.