You cannot possibly stay the greatest country on earth without skilled migration, unskilled migration needs to be contained and measured against requirement but even there, western countries have aging entitled populations that would rather live on welfare than work. Musk is a massive asset to the US and he's a skilled migrant, there are many many more. Economies are like sporting teams you need the best players to win no matter where they are born, attracting and retaining talent like in sports are key to the success of your economy.