Frankly, defense stacking vs. percentile penetration + shred isn't even viable nowadays; it's just too inefficient and you still get peeled like swiss cheese. Flat damage reduction and health are among the better defenses but of course percentiles still exist, so...
Well, actually... Vayne is fairly weak against ADs and some mages but she's quite a strong laner vs. bruisers. That's why she's the second preferred AD carry in addition to Ezreal on both Treeline and Dominion; low CD dash + invisibility + knockback with a potential stun is a just an amazing kit for keeping distance and she's got extremely high inherent sustained base damage (compared to Graves or Corki who have great burst but relatively mediocre sustained damage comparatively especially early on; burst is great vs. squishy targets but sustained damage is the king vs. tanky targets).
Her principal issue of course is her escapes; she's not very good at those vs. ganks since she's so squishy. But like, in 1v1 she can just kite around vs. e.g. Jax, when he uses gapcloser, Condemn knocks him right back alongside a potential stun and on 6 you have stealth Tumble kiting available to you too.
Yeah, but the reason you even went Philo is to get the GP10 in the first place. I mean, otherwise you'd just get Items That Do Stuff or Catalyst or Doran's or w/e.