What I never get is why or how Dorian is supposed to be a "pariah" and a "rebel" and someone who wants to "change" Tevinter. He was advertised as such, and he talks about how much he loves his country, and then sometimes makes fun of it, its history, system of government, etc. but what is so rebellious about Dorian?
All I can fathom is that his being gay makes him a rebel. His personal quest is pretty much only ABOUT him being gay, so what else is there? He doesn't seem to think there's anything wrong with slavery. He laughs at the assumption that there are blood mages wildly roaming the streets of the capital. At most he will fuss about social traditions and familial expectations regarding inheritance.
Is Dorian the only gay man (or gay woman for that matter) of his social class to have ever refused an arranged marriage? Has no straight person ever done that? (No young Tevinter girl has ever told her parents NO she will not marry the creepy older man just to propagate the magical strength of their families? Really?) And why did Dorian have to leave the country? (I'm assuming something to do with Felix and his dad? Supposedly he has broken with Alexius. So did he follow him? Or has Dorian left Tevinter because he's a "pariah"? What sort of pariah? WHY?)
His story is just so sadly shallow. :-\ But as someone else pointed out, the same goes for many of the DAI companions.
Dorian's theme is "The Redeemer" so he's all about saving Tevinter and showing the audience that not every Tevinter Mage is a crazy blood mage. He did rebel though. I think the WoT mentioned him getting into fights, excessive drinking (as we've heard in game), and going to elven brothels. He did get kicked out of the house but no one really knows the timeline of when it happened. He was recruited by Alexius at the brothel I think, then went to work for him, then chased after him to the South. But somewhere in between all of that he must have went home, refused to marry again, and got disowned. I bet Papa Pavus wished he had choked it up and banged his wife for another kid. 
Seriously, seems rather pointless to disown your ONLY son when you need him to inherit the family fortune. smh.
I wouldn't say Dorian's story is shallow, he has some depth to his character and he does offer up a different side of life for Tevinter. It's just that his personal quest emphasized his sexuality which overshadowed the other more important themes and it came across as a more modern day Western LGBT plot than a Dragon Age plot. It's just another example of how fickle DA lore is, but it's extremely minor in comparison to the rest of the plot and not even as worst as some of the other companion personal quests.
I would say this, DAI had the most uninteresting and un-fleshed out personal quests in the series overall. The only ones I liked were Solas and Cole's. Cass' loving Varric's book was funny but I don't even know if that was a personal quest. lol!
Edit: I like Dorian's personal quest too, but more because of my own head canon rather than the DA team's writing...and also because Ramon worked wonders with that dialogue.