Classical theism was always a motte-and-bailey, but it's very strange in that the motte is perhaps harder to defend than the Bailey. The problem of evil is the best argument against the theism that most theists actually hold, but as you say, the best argument against classical theism is its own incoherence. To say that God is not a being is logically equivalent to saying that he doesn't exist. To say he has no properties means he doesn't have any of the properties theists attribute to him. They try to get around this by saying he has them, just not in a univocal sense, but this is pure nonsense - in order to have the properties we attribute to him even in an equivocal sense, he must have properties similar enough to those properties to justify the equivocation.
This gets even worse when you consider that Christians believe humans were created in the image of God. That doctrine flatly contradicts classical theism, since it holds that God has something in common with his creations. And not just some random thing, but something so important, so central to his and our identity, that it can be called his "image."
The story analogy also fails because an author doesn't exist within the world of their story. They exist in real life only because the author isn't real. To say that God is like an author on an ontological level, then, is to say that he doesn't exist.
Classical theism was always a motte-and-bailey, but it's very strange in that the motte is perhaps harder to defend than the Bailey. The problem of evil is the best argument against the theism that most theists actually hold, but as you say, the best argument against classical theism is its own incoherence. To say that God is not a being is logically equivalent to saying that he doesn't exist. To say he has no properties means he doesn't have any of the properties theists attribute to him. They try to get around this by saying he has them, just not in a univocal sense, but this is pure nonsense - in order to have the properties we attribute to him even in an equivocal sense, he must have properties similar enough to those properties to justify the equivocation.
This gets even worse when you consider that Christians believe humans were created in the image of God. That doctrine flatly contradicts classical theism, since it holds that God has something in common with his creations. And not just some random thing, but something so important, so central to his and our identity, that it can be called his "image."
The story analogy also fails because an author doesn't exist within the world of their story. They exist in real life only because the author isn't real. To say that God is like an author on an ontological level, then, is to say that he doesn't exist.