OP, to me it appears that some people (I don't know how many there are but I've met a few) have some trouble conceiving of a mythology within a fantasy world actually being nothing more than mythology because it's a kind of "two times removed speculative reality". It's a phenomenon I've seen all too often: people who are skeptical about religious claims in the real world suddenly losing that skepticism when being presented with religion within a secondary world, particurly if it's fantasy.
As I see it, the Maker is just as speculative as the gods of real-world religions, and if the so-called Old Gods have any plausible claim to the designation "deity" remains to be seen, since whether or not they are dragons, we don't even know if they're intelligent. Most importantly, statements of believers about the veracity of their own faith's mythology are by definition suspect since usually no independent evaluation of their claims is possible.
That the Chantry teaches something says nothing about actual history. Where the Chantry's teachings are historically accurate, that's only where history fits its ideological bias.
An example: we know the Chantry's teachings about darkspawn, the old magisters and the Golden City from as early as DAO's intro. For all of DAO and most of DA2, that was just a story with no claim to historical accuracy. Its role in the Chantry's ideology was obvious, and thus we were well-advised to be skeptical. For me, it was just your typical despicable cautionary tale designed to make people obey and not question the status quo.
When we met Corypheus in DA2:Legacy, that was the first believable evidence we had that some of Tevinter's ancient magisters indeed attempted to reach a place in the Fade they knew of as a Golden City. So now we know there is some historical accuracy hidden within the Chantry's story. Still, any other claim made about those events, particularly that the City was the home of the Maker, remain just as suspect as before. That the old magisters were in over their heads appears rather likely, but the fundamental value judgment of their actions as acts of hubris, as well as the claim the taint is ultimately their fault, is all too obviously in the interest of an organisation that wants to take or retain control of the prevalent memes about what can and can't legimitately be done with magic.
@cronshaw:
(1) The existence of one fantastic element has no bearing on the likelihood of another one existing. In fact, the "standard attitude" with which to approach any new world is "everything is like in the real world unless shown otherwise". Without that attitude, we would become lost in the fictional worlds. Religion, particularly Andrasteanism, works all too obviously very much like real world religion.
(2) From an in-world perspective, these elements - elves, dwarves and magic - are not fantastic but natural. The existence of a creator god is a culturally dominant meme, similar to how it was for large parts of European history, but that says nothing about the actual reality.
(3) That something came into existence does not in any way imply agency or intention. Specifically, the creation of the darkspawn might as well have been an accident intended by nobody. Even if it was intentional - which I personally believe - we have no idea whatsoever about who did this and why (unless it was Dumat). Particularly, there is no evidence at all that some entity was involved which has enough attributes in common with the Chantry's Maker to be considered identical.