Basic Action Super Heroes!

advantage - 1pt and target gets -2 dice modifier for soak roll vs the attack

a +x1 dmg gives 7pts on average and can go higher with a good roll or a hero die

a -2 dice modifier vs a soak of 4 reduces their soak by -8.

by being a dice modifier, armor piercing is less useful against low soak foes and very useful against high soak foes.

that soak x7 foe loses -14 soak from armor piercing

I usually do this with an enhancement [Extra effect +2DM vs. Armor] but there's nothing wrong with coming up with your own way. The advantage of your method is it will work on people who don't have the Armor power.