It is impossible for them to make Saudi Professional League as a big league like either La Liga or Premier League. Because you can not have a big league with very old players like Benzema or Cristiano, Kante. Those old players can bring some lessons to domestic players in Saudi but their performances will not be as same as when they were young years ago.
If Saudi Professional League can have players like Mbappe, many of such young super star players, they can increase the league quality a lot. Unfortunately it is impossible to convince players like Mbappe to join the league. They will want to play in Europe and win Champions League, Ballon d'Or, money is not all they want.
Young players can not grow up to super star players if they only play in Saudi or South America countries like Brazil, Argentina or Uruguay. We all see those youth players try to find their future in Europe. It is impossible to convince youth European players to join Saudi Professional League. They must build the league with their local players and players from Middle East nations.
They are not really aiming at being that good, they are aiming at top 10 for the time being, and in order to do that fame would be enough. They started this path with getting Ronaldo first, and that's a big enough name that he could make others come, now they have a few more, and that will make it so that they could get a few more.
There are a lot of great players you could convince with just 10-20 million a year, and they could get those players. This is why I honestly believe that they are going to spend a lot of time finding the right players. When they do build it, which won't be in a single season, they will be able to get into top 10, even if 10th, and that's not impossible to achieve if you spend enough amount of money.
They still won't easily overcome the problem that young and strong players won't give up a career in Europe for 10-20 million per year in Saudi Arabia because they can earn that money in Europe already. The price will stay very high for Saudi Arabian clubs to get players who are in their prime and who are outstandingly strong. Take Bellingham as an example, I wonder what a club from the SPL would have had to pay him in order to make him waive the offer from Real Madrid at this stage in his career only because he can earn more money in Saudi Arabia. He would give up on everything he dreamt of. Playing for Real Madrid in the Champions League one day and win the most important trophies in the world. Even when they paid him 50 million, he wouldn't have decided to go to the SPL. It will remain expensive for them and that can't be sustainable forever.