Citizenship can be either jus soli or jus sanguini. It's jus soli when a child is born in the US, and jus sanguini when he's born overseas. I don't see why you find this so odd or "inelegant."
It’s odd and inelegant because it lacks precision and is not rigorous, in a document of such serious import as our Constitution.
You’ve acknowledged that the several States determined birthright citizenship differently, curiosity.
There was not a State in the nation, that would have deemed a Presidential candidate born abroad of citizen parents eligible.
And, there were several States that would not have deemed a Presidential candidate born in one of the several States eligible, if that candidate was born of a foreign father.