I question that "Someone must've created it" is the default assumption in absence of any real knowledge. Creator gods always run into the question of who has created them, and if nothing has, then given the absence of evidence, the same assumption is more plausibly made about the world in the first place. So while not exactly illogical, a creator god is certainly a very odd claim to make. Other gods don't run into the same kind of problem, though in both cases the main question is "are they deserving of worship?" - which is what this topic is ultimately about.
I wouldn't want to be co-opted by an ideology that counts someone as worthy of worship if I don't. I can't have complete control over how I am perceived by the world, but I want a say in it.
Getting more into the matters of DAI's story, another question is "are we supposed to associate 'Andraste' with that Fade spirit in the trailer?" I say the story is highly suggestive in that regard and as such appears to support a religious angle much more than a non-religious one which would regard the Fade as a dimension in which what people believe can become manifest, and the spirit owing its appearance to that fact.
Well from a theological perpective God is God because he created everything. You can ask "But who created him?" and that would be a fair point but again that's why he is God. Every cause has an effect, and every effect generates another cause, and on and on. God would be the effect without a cause, or the cause uncaused. God simply is, he is a timeless and spaceless intelligent being that created time and space - the universe. So beings like us humans living in the universe and are bound by its laws could not even understand something that is outside their little bubble and is not affected by the laws of the universe.
Now in the world of Dragon Age does the Maker deserve worship? this is a very interesting question because reading the lore we see that even though the Maker is inspired in the judeo-christian God the Maker is nothing like the judeo-christian God.
The Maker seems to be very whimsical and distant, he doesn't seem to care much about mankind. Even his attributes seem to not be too godly at all but I guess that's what happens when the God of a fantasy world is thought up by people in a desk. Any God invented by people tends to fall short if you compare it with the real deal.
With the introduction of The Elder one, who seems to play the part of Satan, it seems that Bioware wants to point at the existence of the Maker, after all when the bad guy says that God doesn't exist you know God exists. But they won't show undeniable proof of the Maker or Andraste's existence (as his "bride" at least, Andraste existed in the world of Dragon Age) because they want to please all audiences, atheists, agnostics and believers. They will leave it as a mystery and up to player interpretation.