Debunking the Physico-Theological View | Lack of Religious Definition

In the SD
Hello Rabbi, what do you think about the following claim (taken from the heresy forums on the internet)
When the believer claims that there is a God as an explanation for the creation of the world, its beauty and complexity.

In such a case, I simply ask: Define "creator." What is it? What is its essence? Where does it come from? What is it composed of?
If he starts telling me that the Creator is "spiritual," I ask him, "Define spiritual." He starts telling you about all sorts of other worlds that exist outside of space and time….and I ask him, "How do you know that this exists? What is the source of your knowledge about all sorts of "spiritual" worlds? Somehow we arrive at the conclusion that the source of all knowledge about spiritual worlds is someone's imagination, past or present.
That is, the "Creator" and all the "non-physical" worlds are simply figments of the human imagination and nothing more!

What does the Rabbi think about this? Is there no problem in using this hypothesis without explaining its essential nature?