If God is all and God is good, then the lack of God would indeed be the lack of good.
But I think evil may require deliberate intention somehow, to 'kill' the good? I don't know. It's just speculation.
"Forgive them Father, for they know not what they do" Wiser heads than mine have debated it for millennia?
The point is imo that true polar opposites, like fire and water, or electron/proton do not explain light and darkness -- where darkness is not the opposite of light but just the lack of light.
But nor do darkness and light explain good and evil?
EDIT
In criminal court, after considering mitigating circumstances, a judge every now and again will say to the accused: You are purely evil.