So shields should take true damage just so your nuke hits harder? Just doesn't feel needed, Especially since a lot of supports are the ones who shield, and they don't have the money to invest in the items to make the shields scale. Using your targets armor/mr is the only thing that keeps the shield worthwhile in the later stages of a game.

Creativity Based Logic Destroyer: A shield is actually a skin-tight barrier that exists beneath all forms of armor and cloaks. Some may create a visible bubble, but the essence of the shield goes all the way down to the skin.

Seriously, logic in a video game? You expect too much of a world with 3 foot tall furry cat men. Also my carry shoots a gun with unlimited ammo and somehow uses it to shoot out 3 swords and a bow with every shot. Is that logical enough for you?

Edit: also, shields in their incarnation have always been and will always be analogous to temporary hit points. It is a number that can exceed your maximum hit points and they are damaged first.

Why are you focusing a tank that has been shielded in the first place?