I understand that we should not take ourselves as evidence of anything, there is a huge number of flights and flyers and the average risk of anything happen is not known to us.

It has happened to me (once in 3 years, approx once in 8 one way upgrades), which is why I have less faith in them, as said.
Also, on the routes I go, I rarely see a J cabin with seats left. Sure, I cannot know if there were seat available for sale and they filled it with upgrades. I do know that I have had trouble getting upgrades clear for HKG-route and been told the cabin was sold out weeks before takeoff. Again, that is just my numbers, doesn't prove anything.