While everyone knows that armor is a trap stat against crits,
It's not a trap stat.
Armor reduces all physical damage by a percentage.
Critical strikes increase most physical auto-attack damage by a percentage.
Add on that Randuin's and Warden Mail don't do anything with their passives against crit strikes
Critical strikes are delivered by auto-attacks.
The faster a champion auto-attacks, the more they critically strike.
The slower a champion auto-attacks, the less frequently they critically strike, and the less auto-attack damage they do.
This gave me a thought: What if there was an armor item that was cost-inefficient against AD casters and BoRK, but good against crit strikes? It would have a passive that reduces total damage taken from crit strikes by, say, 10-15% (like the mastery), but if your opponent doesn't build crits, that passive is wasted.
It would be awful.
Armor, Health, and %AS slows all increase survivability against attack damage, attack speed, and critical strikes together.
Targeting critical strikes specifically is only good against critical strike damage modifications specifically.
And only a very small number of champions actually start the game with critical strike chance.
Crit isn't something like HP, HP/5, AD, AS, Armor, MR, or MS that all champions come with.
Starts at 0, so all anti-crit mechanics start at 0.
Marksman are generally the only archetype you can count on purchasing crit at all (most tanks, fighters, assassins, mages, and supports don't rely on crit).
On the off chance the item was actually powerful enough to be worth grabbing (outside of vs. Yasou matchups), the meta would simply shift so the only champions played as marksman weren't reliant on crit - making said item worthless again.
It's worth noting caster-heavy, AA light marksman like Corki, Ezreal, and Lucian have dominated seasons 1, 2, and 3.
