I'm well aware of this, since I have close family that your situation applies to. Actually, if your parents are married and even one is a US citizen, you will be too, always.

This may just be a terminology disagreement, but that's typically not what is considered "citizenship by descent".

What we're describing is considered by the US to be "citizenship by parents" or "acquired citizenship". On the other hand, "citizenship by descent" is the European tradition of awarding citizenship to grandchildren and even great-grandchildren of citizens. The US doesn't have citizenship by descent (in fact, it's true that there's a single situation when your grandparent's citizenship can matter to someone trying to assert US citizenship, but it's only as a kind of "tiebreaker" if your parents weren't married and one was a US citizen).