"The idea was that an unconditional surrender drove home the point that one side had truly lost and would accept it."
I don't recall this idea being evoked, but it makes some measure of sense. In practice though, in World War II, it also drove the point home to Germans and Japanese that they needed to keep fighting. And that brings us back to the hypothetical choice between a long invasion and the bombs.
Anyway, it wasn't my intent to debate this. It's the wrong venue, even if I had a particular desire for it. Which I don't.