Are they really less tenable? Because, if there be a God, on the judgement day present in many of the religions we know, he might point out that the sheer complexity of the universe should be a sign of his existence. What are the odds? Are the odds actually in favor of man's theory, or is man desperately clinging to a theory to avoid him? Is it actually good science as designed, or rather any excuse no matter how implausible will suffice? Good science looks at the odds and makes a conclusion. Bad science looks at the conclusion and ignores the odds to bias towards a result.

Edit: Furthermore, this said God might point out on said day the lack of any aliens, or other life, as another sign that the universe was made for man, and nothing else, and the sheer enormity of it should be yet another sign. For if the universe was not large, would it be more easy to deny?

Edit 2: You might dismiss the above, and these aren't the best arguments that could be formulated, but it is more to show that your presupposition that a larger universe disproves his existence is untenable.