Armor and Penetration
So it seems as though AD assassins (pretty much just Zed in all honesty) can get ahead relatively quickly by focusing all their gold into a Brutalizer early on, and that's cool.
Now the not so fun part is stacking penetration. Like yeah, they're squishy, but it doesn't matter if they've killed your damage source. 60% reduced physical damage feels like much less when the enemy assassin has a Last Whisper AND a Black Cleaver.
Can armor pen be capped to a certain number or percentage? I feel like this is the same principle as to why we don't have 100% cdr, but I'm probably wrong.
EDIT: If anyone has any tips for dealing with this in game, I'd love to hear them.