Bottom line:
Saudi Arabia is a mess. Oil cannot possibly make them a superpower. They will run out of it someday. Hence, economy cannot be sustainable for a long term and most of their engineers will become jobless.
Secondly, its not like we are seeing Saudis working day and night. The fact is most of them are lazy a$$. In North America, a lot of people work from 8 to 8 regardless of whether you are know to be as an immigrant or non-immigrant. Everyone is equal. Clearly, this is not the case in SA. Once expats leave the country, they will be in ruins.
A lot of Saudis will argue that they own a lot of foreign corporations and it creates a beneficial impact. The truth is, economy is not getting any better in the West so once they go bankrupt, naturally it is also a loss in Saudi Arabia's favour.
Thrirdly, they have got a lot of gold reserves in USA. We all know (except Saudis) that American people in general are opportunists and they always have conditions. If the time comes when Saudi Arabia will need it back, American will refuse. its as simple as that...
Fourthly, Saudi Royal Family is corrupt. If a country like Iran, Pakistan, and India have the same amount of money that Saudi Arabia has now then we will see far more sustainable developments. The development in Saudi Arabia is artificial, 100% like UAE. They will start copying building skyscrapers like Effiel Tower and CN Tower. A country becomes a superpower, if its unique or when it has its got better and improved ideas own its own to make their economy successful.