Definition: Let us take ‘cosmos’ as a term denoting ‘the universe’, the ‘world’, or ‘everything that we see’, etc.
Statement 1: The cosmos was created and is sustained by an ‘other’.
Statement 2: The cosmos is all that there is (and ever has been and ever will be).
Both statements assume the above conceptual definition of ‘cosmos’ (‘everything that we see’), but only statement 2 depends on knowledge of the cosmos that we don’t have, and will never have. In other words, the theistic statement (1) doesn’t rely upon complete knowledge of the cosmos, but the naturalistic statement (2) seems to.
It is worth pointing out that this statement (classically expressed by Carl Sagan: “The universe is all that is or ever was or ever will be…“) is in a positive form, but with a negative implication implicit in it; namely that there is not anything other than the universe. Even stating a negative in positive terms doesn’t make it provable.
By way of (crude/imperfect) analogy, this is like someone saying, “Earth is the centre of things” – one could understand the observations that would lead someone to think that.
By reference to a (much better) analogy, this is like a 2-dimensional square saying, “Flatland is all that is, or ever was or ever will be.” One could understand the square’s 2-dimensional argument. How fuzzy, awkward, and speculative 3-dimensional fables, ‘experiences’ and ‘logical arguments’ would seem! Spheres!? Cubes!? Thick-ness!!?? How utterly devoid of any solid, ‘objective’, 2-dimensional ‘evidence’!