It is more complicated. Modern violins can be louder, and audience generally think loud=better, but this may not what the player prefers or what is wanted in an orchestra. There is also the issue of playing an instrument only an hour vs playing an instrument for a tour or longer time.
https://www.violinist.com/blog/laurie/20121/13039/
This is a description by one contestant who participated in the 2010 test. She generally likes that new violins can sound really good, but she criticizes:
> As for the old violins: one was a Guarneri del Gesù (circa 1740) and two were Antonio Stradivari (circa 1700 and 1715) "These violins were loaned with the stipulation that they remain in the condition in which we received them -- precluding any tonal adjustments or even changing the strings." That means that, whatever happened to the old violins during their trip -- if they got jostled on the airplane, etc. -- there was no soundpost adjustment, no bridge adjustment, no check for open seams. If the strings were a little older, they were a little older. … My concern is this: it sounds to me like the older instruments were not optimized -- by either selection or by luthier adjustments -- while the new moderns were.
There are also differences between Stradivarius. In the formal test one old Stradivarius was universally disliked and in an informal test a modern violin beat an old strad. She wonders if that was the same model:
> […] During the same event when this study took place, another more informal "study" was done by those who did this one. While jurors were deliberating over the outcome of the Indianapolis violin competition, the audience that was gathered was asked to evaluate some moderns vs. old Italians. Indianapolis Symphony Concertmaster Zach De Pue played four pairs of violins, allowing the audience to decide which they liked best of each pair, based on playing excerpts from "Scheherazade" and Strauss's 'Don Juan.' Each pair included one old and one modern violin. The votes were very close each time, but ultimately the audience chose one modern violin and three Strads, from the years 1699, 1714 and 1715. Several more tests and votes narrowed the fiddles to the one the audience liked best: Jimmy Lin's 1715 Strad. (Was that non-preferred Strad from the study in the mix? I'm guessing it was, and it was the one not-preferred).