Evolution is just a theory. By that reasoning, belief in a Biblical God is also a theory at least to non-believers.
That seems to make the usual mistake - it confuses the general lay definition of "theory" (a guess) with the scientific definition (a testable and falsifiable hypothesis).
As a scientific theory, evolution via biological descent is about as much of an established fact as it can be. The basic theory of evolution has proven incredibly robust and currently influences many other scientific fields. And according to some experts, even not-so-scientific fields like economics.
Anti-evolutionists mostly ignore all that, and continue to harp on Darwin's original writings from 150 years ago. But unlike theology, scientific literature isn't graven in stone forever. It moves forward, continually trying to falsify its theories to see if they are valid or invalid. That's what science does. That's what science IS.
The belief in a Biblical God will never be a scientific theory because it can be neither tested nor falsified. I've seen many, many believers claiming to test the theory, at least on their specific god. But I've never seen a convincing test for any god, unless Mr. Occam has recently started shaving with a chain-saw.
And a falsifiable theory of a Biblical god? That's called "heresy."