I think the decision of the Government or Investors to bring many star players and legends to the SPL is the first step to attract the attention of football fans from all over the world. They have unlimited money so they can do that. Now we can see that the SPL is already known by many people. Some football lovers in my country even have a collection of shirts from Al Hilal, Al Ittihad, or Al Nasr.
But on the other hand, the arrival of many star players to the Saudi League does not immediately make Saudi Arabian players one of the football powers in the world. I remember Mancini once said that Saudi Arabia had difficulty in qualifying because most of their players were bench players because teams in the SPL preferred star players from Europe or America rather than local players. Of course this is something bad for the Saudi Arabian national team but I am sure in the long term they will become one of the best teams in the world. Maybe in the future they will become the number 1 or number 2 best team in Asia along with Japan.
The reason for the huge investment in the local league is to show the world that Saudi Arabia is opening up to the world. Another reason is to groom players. The third reason is to win the World Cup host bidding. The government seems to have achieved the first and the third goals but failed to improve the quality of the Saudi national team.
I wish you could add the link where Roberto Mancini made that statement. This is because the Saudi Professional League has a policy that limits foreign-based players in every team to eight. It might be high but Saudi players are still the majority in all clubs. Maybe the impact will be felt in the future.