Just as many of those religions also have major gods that did create the world and can only be defeated by other gods. If the Maker or Creators aren't real, I'd be curious to find out exactly what created the Fade and spirits. Unlike Earth, there is no scientific explanation for where spirits come from or why anyone has supernatural powers, so atheism is a lot less plausible. I'd be interested in learning the truth, whatever it may be.
Assuming that the Maker is not real without scientific evidence to explain the nature of the world makes little sense to me. Either possibility could be true with what little we know about magic and the Fade.
You are right, still I fear you missed the point I was trying to make.
The point is that in a similar context, where even some humans are able to perform supernatural feats and demons and spirits are very much real and the most powerful amongst them are what we would call a minor divinity: does it make sense the concept of a god?
You can imagine something more powerful than the spirits you know of, still the Fade is far from "explored" and if your only criteria to differentiate a god from a spirit is power you must first know what is the most power a spirit can have.
Thus, yes, real world atheism is not applicable to Thedas, but so is real world religion too.
Both cease to make sense for Thedas is a fantasy setting.