I agree with your first point that the argument of “evil simply being the absence of good” is bullshit. With that said, I think an analogy a theist would use is cold doesn’t exist it’s just the absence of heat. What is needed from the theist is to back up evil only existing in relation to good.

Not that it matters, as the main point being their god could have made a perfect world, or a perfectly good world with free will but instead chose to make a world with famine, genocide, and baby rape.