The point here is - if god created the universe, then he has interacted with the universe. As such, we should be able to detect god in some way - i.e. through that interaction.
If god is the reason, solely, for
something rather than nothing OR
time without beginning, how would we go about detecting such a god ?
If he created the universe, but there is no trace of it, then you are once again left with an unnecessary god...
If god "created the universe" then, of course, god exists. Period. Whether or not there is
any trace of god in his creation would be irrelevant. Whether or not god was
necessary depends on whether or not it is possible for the universe to have come into existence without god. Therefore we can only conclusively dismiss god as being
necessary once we discover how the universe could have existed without him. That still, of course, would not exclude him from existing, just that he is not
necessary.
...same as our unecessary atom-fairy from before. You say it did something, but define it as being impossible to detect.
Well,
you said it did something. But what exactly....
As leaving this god out of anything will not reduce our understanding in any way, we can safely assume that this god does not exist to the same degree as we can assume the atom-fairy does not exist.
But, does the atom-faerie actually do anything that needs doing? An atom decays randomly. Do we need an atom-faerie to determine which atom decays next and when? I don't think so. It's just a random event. You've posited it as doing something that doesn't need doing.
On the other hand, no one knows the answer to the ultimate question of our existence ("something from nothing" or "time without beginning"). In other words, god is posited as being the answer to a question that has not yet been answered by science.
Remember that I am not championing god, nor suggesting there is any evidence for god's existence, nor that the above is a sufficient reason to believe in god, just that he can not be as easily dismissed as the tooth faerie (or the atom faerie).