> 2. The operative assumption in my statement is that the government does not possess the key. If they do possess it, all bets are off.

All bets are off from the start. At some point the CIA managed to get their hands on the French nuclear keys…

> 3. This thread is about a hypothetical situation in which the Korean government did store backups with a U.S.-based cloud provider

This thread is about using US cloud providers, that's it, you are just moving the goalpost.