I was reading up on Stradivarius instruments on Wikipedia.
From what I read, quantifying if and why these particular instruments sound different or better than others is kind of like trying to do the same with fuses in hifi gear. Clearly part of the story here is the legacy and historical impact of these instruments which are very valuable as a result of reputation and age.
Its one of those cases where clearly there may be physical differences from other designs, but quantifying the sound quality remains elusive.
Clearly, few every day shlub musicians would play such an intrument in public or be recorded playing one, so I suspect the skills of the players overall contribute to the instrument's reputation.
I have to believe its possible to make a modern violin that is at least in the same league as one made 100s of years ago. IT might sound similar or different, maybe even better, at least in some ways to some?
I am a firm believer that time always tells though when it comes to practical assessments of value or quality. Good things last, bad things tend to run their course for the most part, but there is always something new on the horizon.