But if we assume he does exist, then he explains everything.
Neither assumption is helpful or explanatory. You're not explaining anything by assuming either way.
Even IF we assume a creator, and I ask you how something works, saying "God did it" explains nothing. Even if we use the favorite theist example of the watch, if I said ,"Hey, cool watch. How does it work?" If you kept saying "Timex made it", I'd say "I know, but how does it work?" "Timex made it." "I know, but how does it work." "Timex made it." "I know, but how does it work?" Ad infinitum.
"God did it" is not a useful observation or assumption in any sense. The assumptions are irrelevant at best. I challenge you to provide any example which proves otherwise.
I think the best way to reach an understanding of a new concept is repetition.
Mechanism is one thing. Agency is another.
Let this ring back and forth in your mind for a while. Then, remember that explanation of agency is never meant to provide explanation of mechanism. This is where atheists most often become confused.
As for the underlying assumption of whether or not God exists, you and I can only choose between the two. There are no other possibilities.