A solution to % Penetration

As it is right now, Void Staff and Last Whisper are probably the highest damage spike items in the game against all types of enemies, even early in the game, or against enemies with little resistances, they still offer huge amounts of damage for a very low cost. The solution? Make them scale.

Last Whisper:
40 AD
Unique Passive: Gives 20% + (.1 * Bonus AD )% Armor Penetration

Void Staff:
70 AP
Unique Passive: Gives 20% + (.05 * AP)% Magic Penetration

The numbers are not perfect but I think it's a good starting point. It reduces the effectiveness of rushing these items and getting huge power spikes. It also reduces the power of tanks buying only a void staff or last whisper but still being able to do large amounts of damage thanks to high bases. This also helps counter mega tanks end game, as it allows for champions that build high amounts of AD or AP to have more penetration. All in all it really helps with the idea of, the bigger your offensive numbers, the bigger your damage will be.