I've scoured enough sites (most being reliable ones) and can now safely say that it indeed HAS been proven that Cynthia's pokemon are 6 IV. It's not a myth. People have hacked to "catch trainer's pokemon" and get Cynthia's Garchomp, which was tested positive for perfect IVs.
I also verified that Blue's pokemon are not all 30 IVs (through personal testing), and the next most logical conclusion is that it's randomly assigned, like any other trainer.
My answer is finalized now, backed with solid facts.