Stradivarius instruments deserve being put on a pedestal for historical reasons. Stradivari basically defined the sound of the modern violin, using flatter arching and f holes with smaller hole areas than the Amatis, which resulted in a significantly more powerful instrument that was better suited to playing in a concert hall (vs. the chamber music of earlier times). Stradivarius violins are also noted for their extremely fine craftsmanship and attention to detail. The majority of modern violins are still modeled after Stradivarius examples (with a probably smaller number modeled after del Gesu instruments and some other makers). Most top soloists play on (heavily modified) Strads, and so it seems pretty clear that, at the very least, Strads are not holding any soloists back - and that is not the case for Amati instruments, for example, which despite being coveted for their age and history just don't have the same power and sound projection as Strads.

But, as other comments have said, there have been at this point a good slew of blind tests, and Strads are hardly ever recognized better than chance when compared to modern instruments, even when played by experts and judged by experts. People have been studying and modeling after Strads for so long it would be pretty shocking if we couldn't make instruments that sounded as good. In my mind that doesn't make Strads any less valuable - an original Picasso is still valued so highly because it was created by the master that invented Cubism, but that doesn't mean that a modern painter couldn't create a Cubist painting that was "just as good", objectively.