Pondering your remarks, I think you are totally correct. I think the "technically correct" view will confuse people, but I like it.
First an analogy. People naturally view property as the right to possess. But the true nature of property is the right to exclude others. US citizenship can be viewed in a similar way.
The default is that the US will defer to some other source of citizenship. In the US, originally, this was citizenship in one of the several states. For birth abroad, if some other nation grants citizenship according to its laws, the US won't (and actually lacks the power to) monkey with it.
Looking at things that way resolves issues such as citizens on sojourn.
There may be legal customs and norms associated with soldiers abroad, too; although following the default rule, the host countries' citizenship laws have play.
Thanks for your patience and tutelage.
Read a few days ago there were ‘antenatus’ citizens.
Anyone serving their country in uniform can not be held to have quitted their country and their allegiance to that country. The only way a child born of someone serving in the military abroad is of that person who is serving married a foreigner while in a foreign country. Otherwise, according to the law, a child born to 2 US citizen parents while in service to their country abroad, that child IS a natural born citizen and anyone who says otherwise and NOT done their due diligence. And this is why McCain was eligible, it had nothing to do with where he was born but everything to do with who he was born to.
I was chatting with a lawyer the other day on this matter and he predicted that one day a US citizen baby born abroad adopted by a US citizen couple, might run for president a cause quite a stir.