I may replace 'better' with 'preferable' in your above statement. 'Better' necessarily drags one into a language trap about the meaning of the word. I think preferable is more immune. That said, I agree with the sentiment, and by my definition of fact, elsewhere in the thread, I think your example would count.
I am not quite satisfied with your statement, but I don't know how I could improve on it so I won't criticize. "Preferable" is a better word if you happen to have iron handy and no copper when you need a conductor, but copper is still objectively better — it has a lower electrical resistivity. Saying "preferable" does not save us from the trouble of declaring our values. Hydrogen is preferable if cost is a priority; helium is preferable if safety is most important.