I don't think this has been mentioned yet: we are living in a golden age of instrument building. There are more top-shelf violins, guitars, etc. being produced now than ever before. Heifetz and Elman did not have a lot of choices when it comes to fine, newer instruments. Many players in modern quartets are opting for new violins, violas and cellos.
BTW, Perlman says Oistrakh's strad was a good, not great, instrument FWIW.
BTW, Perlman says Oistrakh's strad was a good, not great, instrument FWIW.