Vayne seems to be overshadowed in preseason, but only because...
Most ADCs would have it better to build damage first, while Vayne simply would work with usual BORK first for the efficiency.
Graves is basically a burst ADC now, so he can simply buy Death's Dance (as one item) and blow her away (or a chunk/most of her hp) each time. Unless I'm missing something with the item-build for Vayne now?
Mind you, I'm not sure if true damage also gets turned into a bleed effect. Or if PD's % damage reduction or damage amp works with true damage. Clarity?
As another point, BORK got nerfed anyway.