Just imagine how scary it would be if they didnt have to grab everybody elses leftovers. And got to work with the elite of the elite talent from the beginning?
They did it once. Got someone named Timothy Theodore Duncan

But I disagree that Ginobili was an obscurity before he joined the Spurs. He was a key piece of silver medalist Argentina team in FIBA 2002 and made the All-Tournament team. He was a steal in the draft of 1999 and joined the team after 2002. And Parker, while a lot more unknown than Ginobili, was a steal himself.
While I agree that Spurs are doing a great job of maximizing one's potential, Parker and Ginobili were meant to be great players almost anywhere in the league.
That said, we can argue that they would have ended up without those rings and have a relatively undecorated career.