"in fact, if someone else DOES stumble on it by accident, it should be considered de facto evidence that the patent isn't novel."

You have industry support for this idea:

“The idea that I can be presented with a problem, set out to logically solve it with the tools at hand, and wind up with a program that could not be legally used because someone else followed the same logical steps some years ago and filed for a patent on it is horrifying.” ― John Carmack