Nobody is claiming users are the 'final word.' You're speaking as if modders are forcing a rewrite of a series. This is just completely silly.
When you go to the store and buy Inquisition, Cassandra is straight.
When you go to the Dragon Age Wikipedia and look up Cassandra, it says she's straight.
When you ask anyone who's played the game if Cassandra is straight, they'll say yes.
In what universe can you possibly claim modders are the 'final world' on Cassandra's straightness if they have absolutely no power over any of that?
BioWare still has the complete and final word and what happens in Dragon Age. They still have all the power. A mod is nothing more than a person's imagination at work concerning a story with a bit of sweat behind it. And you seem to think that that imagination should be cauterized because thinking anything not explicitly written out in the story is disrespecting the author. Ridiculous. It's the opposite of disrespecting the author.
Where do you even think the BioWare writers get their ideas from in the first place? Largely, by experiencing other fiction. And by thinking about the interesting places it could have gone and the interesting things they could have done with it.