"Sturdy" Resistance

I just read a post about damage, and how building resistances just seems to fall short because how much damage champions are putting out on top of tons of Armor Penetration items.

It got me thinking, why can't we have "sturdy" resistance? Basically a way to mitigate Penetration.

If an item has 60 Armor +5% Sturdy Armor, then Armor Penetration is reduced by 5%. Or some math I'm too tired to figure out right now. And all the scripting involved or whatever.

The point is, there's got to be a way to provide some kind of counter to penetrating resistances.