What's the basis for saying that the "original purpose" was to let companies hire "truly exceptional foreign workers"?

My understanding is that the H-1B was introduced by the 1990 immigration act, where the H-1B is supposed to be for "specialty occupations" other than nursing. But the same act introduced EB-1 and O-1 for people with "extraordinary ability", which sounds a lot closer to your "truly exceptional" understanding. I think maybe you're projecting a purpose onto the program that was never really there. The H-1B quota when it was introduced was 65k, so it's not like it started out being dramatically rarer than it is today.