like % bonus armor pen
This allows ADC's to :
Not burst squishies and assassins
Have predictable consistent damage per second
Still be effective against tanks
Not depend on RNG luck ( for the sake of both sides)
In addition, Riot can tune how different ADCs scale more consistently and they can also come out with more interesting utility-based ADCs that don't overshadow other ADCs. Right now, ADC's do so much damage Riot can't afford to give them any more fun mechanics/ utility because it'll break em.
I know what some of you are thinking; ADCs are already bursting tanks. The thing is, both are currently overtuned. With this change, I think it will bring more balance to the game.