This is so wrong I don't know where to begin.
Oh yes, many high dragons (ie female dragons who make it to old age) are portrayed as being sentient. For example the quest for the holy grail included a segment where a high dragon convinced a bunch of humans to worship her as the reincarnation of Andraste. And that same high dragon tells you that she will reward you if you mix a drop of her blood in with Andraste's ashes. None of that could have happened if the dragon wasn't sentient. The only encounters you have with high dragons indicate that high dragons are sentient. It wouldn't make sense for some high dragons to be sentient and others not, especially when they all came from the same source. The dragons that were worshipped as gods by the Tevinter mages were simply the dragons that desired to be worshipped as such.
One could ask why it is that if all high dragons are sentient we don't see any instances of high dragons living peacefully among society. I think that is more a matter of the authors not really having much time to flesh out or think about the ramifications of dragons being sentient. The authors simply made high dragons sentient and then decided they would all be evil and just want to see the world burn.
And there is actual and direct evidence in the game which suggests that creationism is real in the Dragon Age universe (ie the Fade and the demon/spirit explanation for how they were created).
Oh my......this is so wrong I don't know where to begin.
First, the dragon is not sentient. At least we're never given any indication that she is. It's Kolgrim, her self-appointed high priest or whatever who tells you to mix the ashes with dragon blood, and who tells you you'll be rewarded for it.
Also, we never find anyone who knows their own ultimate origins. It's humans who say spirits are the Maker's first children. Of course they do this without any evidence for it. At least we never come across anything that indicates it might be true. And if the spirits reflect human virtues and flaws, that's because the Fade is a reflection of the collective human consciousness. What people believe, what people dream of, the Fade will reflect in some way.