Rather, it would be "Builders claim their buildings are earthquake proof, and jepson was able to show a subset collapse in earthquakes. The rest may or may not be earthquake proof".
That's still very valuable. It's really valuable to know when something is wrong. It would be more valuable to know that something is definitely right (correct / "earthquake proof"), but jepsen cannot prove that.
FWIW, I think you're raising really good questions in this thread. Qualitative safety is highly contextual, depending on fault model, significance of individual operations, concurrency, throughput, latency demands, operational characteristics, data volume, etc etc., and I try to touch on that in the "Toward a Culture of Safety" section in this report. Hopefully that resonated for you.