*sigh* Dark fantasy attributes realism to the characters. So, for example, characters can die just like regular people in the real world as opposed to Tolkien high fantasy that kills a Horatious. Meaning, all the 'good' characters (or Horatious) must die well for a cause or in a trumped up way (e.g. Horatious 'defending the Pons Sublicius). Bioware does not have trouble when it comes to killing their dandies, but the way that they present this type of thing breaks what could be a dark fantasy trope, by implementing a high fantasy way of doing it. Mordin in ME3 was a "good character", he dies saving the Krogan. King Cailin and Duncan "died well" defending Ferelden by fighting the Darkspawn. Compare that to how Ned Stark died, or how Rob Stark died?
Even popular characters who are bit more ethically ambiguous, but are much liked by the readership can die from a menial thing in dark fantasy. Kal Drogo died from an infected wound. Could you see Morrigan dying in such a way? Could you see Varric or Alistair getting killed by friendly fire? In real life King Richard the Third (or good King Richard) died fighting a bloody civil war, after he took a crossbow bolt to his gut. Could you see Cassandra being wounded in a sketchy close quarters battle, and suffering for hours before succumbing? In dark fantasy a character, who is liked, is just as likely to die from dysentery or by accident, they succumb to death in a way that is more attributable to real people. Bioware cannot seem to do this, hence why I said quirk--you can watch videos of the writers talking about why they killed Mordin (etc) in the "epic way" that they did. As for Dragon Age itself, it is high fantasy with a body horror back drop. It's not true dark fantasy. Lord of the Rings has a type of body horror as well, the Orcs and Uruk Hai. Does that make LOTR dark fantasy?
I'm going to admit that I don't like the fantasy genre in general, so I could quite honestly not care if Dragon Age is considered fantasy, high fantasy, or dark fantasy. I don't care how it relates to Tolkien or Game of Thrones or any other preexisting setting. Dragon Age is a rare example of fantasy that I actually like for reasons that have nothing to do with how dark it may or may not be. For that reason, I'm probably not the person you should be having this debate with.
So...I'll address some of your concerns as best as I am able.
1) Can I see characters in Dragon Age dying in meaningless, horrible ways?
Can *I* see it? Yes, absolutely I can. But I think what you're asking me is can I see the writers of Dragon Age allowing it to happen.
No, I can't, but that has less to do with trying to keep the setting dark as it is a difference in the medium. Game of Thrones and its associated sequels are novels, where as Dragon Age is a game series. The terrible specter of player agency creeps its head in to gaming all the time. When you are reading a novel, you're a passive participant. While you may get attached to characters, you're still ultimately along for the author's ride and you have no agency to influence anything. As soon as you introduce agency to the audience, they will demand greater and greater control over the narrative until we have the mess that we have now, with constant arguments on the forums about how much they should be able to determine exactly what happens and how nothing in the game is relevant unless they have that control.
During the heyday of Origins, there was a significant outcry over the fact that Alistair would insist on taking the final blow against the Archdemon for a female Warden. A good number of players insisted they should have had the agency to take the blow themselves and keep Alistair alive. So, if that lack of agency caused an uproar, can I foresee Morrigan behind dragged behind the Templar barracks and beheaded in a cutscene without the player getting the option to leave her to her fate? No, I can't.
And the truth is, for such a death to be as terrible and horrible as say, Ned Stark's was, you would have to complete take player agency out of the equation. And I can't see a major character experiencing something like that without the player having some means to determine the narrative.
Since sword/sorcery type games are not my preferred genre, I can't tell if other games kill their characters with the same lack of agency that novels do. But I have to ask if this a requirement for the setting to be considered dark. There are plenty of examples within the setting that these characters have realism attributed to them. They are deeply flawed, deeply passionate, none of them perfect paragons or perfect devils. In the examples you're citing, not only do the characters have to die but they have to die horribly or at least suffer.
Definitions of dark fantasy seem to be vary depending on which source I look up. Certain definitions fit Dragon Age as it currently written well enough. So I suppose the next question is, what is the definition of Dark Fantasy that I'm supposed to be judging this franchise by?