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.
Saudi professional league can't get to the level which European football has gotten with the type of players they're going after. It'll take forever for them to achieve that although they can make their league relevant if they continue with how they're spending. Arabic money are already dominating Europe football so they should organize friendly regularly and look for the way the two continents can cross path through football. If the Saudis league can grow ti the level of Serie A then they can use their money to influence a tournament which teams from Saudi and other top European league compete then the Saudi league will be taken more seriously.
As it stands now the Saudi professional league is just been seen as a retirement league for top players and for average players to get the bag they can use for retirement. The Saudi league can't attract players like Mbappe, Mbappe is hungry for success and wants to win everything possible in football and most especially the champions league. He already has the world cup so winning the champions league is now his top priority and also winning the Ballon D'or with other individual awards.