Currently, I'm of the mind that the Magisters of the Tevinter Imperium created the darkspawn to destroy the Dwarven Empire... only, OOPS, their magic control signal - or whatever - got overriden by the (likely unconscious and unintentional) "calling" of the Old Gods and, oh dear, now they're attacking everyone.

Or maybe they were created to cripple Dwarven power AND root out the Old Gods as Tevinter's free labour force? Maybe so the Magisters could do some variant of the 'dark ritual' to acquire that power themselves?
In any case, I don't think it has anything to do with the Maker casting them down and transforming them into monsters in any literal sense. I mean, in the context of the setting I believe in the Maker -- sure -- but I don't think the Chantry know what they're talking about. I see it in much the same way as Leliana does: the Maker reveals Himself in Creation.
(To clarify, I'm not pulling a Spinoza, going all Pantheistic and saying Maker=Creation -- I'm being more influenced by Michel Henry's Christian phenomenology, which is
brilliant. I say that despite being an atheist, too)
As for what the Old Gods are, at present think that they ARE incredibly powerful and intelligent dragons. Not, I hasten to add, "just" incredibly powerful and intelligent dragons. To say that they are "just" powerful dragons is to imply that being a powerful, intelligent and likely sapient dragon does not have the same intrinsic value of being an Old God. In my mind, it does. They are finite beings, certainly, and they're not
God... but from a
human perspective, they are so powerful and mighty that they are, indeed,
gods. It doesn't matter that they don't have a divine rank.

Matthew Stover (awesome author) wrote an
essay on the reimagined BattleStar Galactica (now taken down, d'oh!) in which he says words to the effect of: "
If you're one of those people who thinks that they're not gods but a hugely advanced society with technology that makes them gods in comparison to us... what's the difference? If they're gods in comparison to us, then they're gods." (Paraphrasing)
I agree with that.