Stephen Fry thinks that polytheism is more reasonable than theism, though he believe atheism is the most reasonable. He thinks that if we're going to "endow" nature with deity, then we may as well endow it with multiple gods. Notice how he uses a subjective term - "endow." This is already changing the terms of what theists, especially Christians, are talking about. We are not subjectively projecting our desire for a deity on the world, we discover it. God is not the premise of our reasoning, He's the conclusion. We're saying He's real, not a desire we impose on our understanding of the world.
We believe in God because He has explanatory power. Naturalism, in principle, cannot provide an explanation for the origin of the universe or life. Atheism cannot explain good and evil, beauty and morality. It doesn't have the resources. A theistic worldview has the resources to explain, to answer questions about the world and the feature we observe in it, better than atheism. And the Christian God has the most explanatory power.
Fry muses that theists credit God when we observe beauty in the world, but wonders where God is in the evil of bone cancer and animal suffering. Yet Christianity does explain this in the Fall, sin, and provides an ultimate answer in the Resurrection and new Earth. And Fry is actually inconsistent in his atheism in making this point - as an atheist, how does he assign terms like evil and suffering? If nature is all there is, there is no meaning. It's just a fact that children have bone cancer. It's nature at work; it's not tragic or evil. Christianity does acknowledge and explain the "nice bits" and the evil bits.
He expresses his wonder and marvel at the way nature works, yet if he's right, "wonder" and "marvel" aren't anything special. They don't express any meaning or value because they are simply brain states determined by the cause and effect of molecules in his brain working. "Wonder" is not more significant than boredom. He's using terms and identifying qualities that don't have a place in his worldview.
Theists don't just impose God in the things we don't understand. He's saying it's the God of the gaps, so it may as well be the gods of the gaps. Ancient Greek mythology has no kinship with Biblical theism and Christianity. Their pantheon was filled with gods to fill the gaps they didn't understand. God explains what we understand to be true and real. The more we understand about the world, the more we learn that there needs to be a theistic explanation. And the God of the Bible meets the criteria for the adequate explanation. Atheism and polytheism do not.
The single God of the Bible is the best explanation, no more gods are needed. He's the conclusion to our reasoning, not the gap-filler. He's real and explains the real world, not a wishful thought we endow nature with to give us meaning and value.