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.