1. BioWare isn't required to be "fair" about anything. They aren't required to represent anyone's politics or point of view. The fact that in this case, they didn't represent yours isn't a failing on their part. They didn't allow players to spread slavery, or institute communism, either. Fulfilling every player's potential political agenda is not one of their jobs.
2. Speaking of agendas, including a variety of sexualities, and telling stories about them, is not an agenda, any more than including characters with different skin colours, or points of view is. If Dorion represents an agenda, then so does Cassandra, so does Solas, so does Josephine. Using the term "agenda" to describe the inclusion of a character, or their personal story, is representative of your own politics, not those of the story's writers.
3. The story at hand is a fundamentally heroic one, and the options presented are attached to that notion. There weren't a lot of "dark" or "Renegade" options this time around. That doesn't particularly bother me, but it is a legitimate criticism to point out that options for behaving in a less than altruistic fashion were fairly limited this time around. If you weren't specifically focused on Dorion's homosexuality, I might have been able to believe that this was your criticism, but by making it about a specific political issue, it sounds more like you're the one with an "agenda."
Note: The above does not have anything to do with my personal opinion of the quality of the story, which is mixed, like most people's.