It is different because people are allowed to do what they want in contrast to being possession.Chivaliers get away with things because they have special privileges not because others don't have rights. Blood magic "prohibition" in tevinter is laughable at best, that "law" is probably only carried to take out rivals , pretty much people that were in tevinter confirmed that blood mages openly preform blood magic and sacrifices at their parties and yes they do Fenris was witness.
What means nothing because Tevinter treats humans as crap as well , only exception are mages wait not even mages, only noble mages.
It doesn't not matter whether taint existed before they went to the black city what matters is that they were one who brought it to Thedas and started blights in process. Their power hunger fueled it and magic allowed to act upon that causing blights.
Lets see
Tevinter:Slavery , impossibility of advancement on social ladder unless you are mage , Blood magic , puppy kicking nobility , abomnations and experiments on people.
Orlais: Ahole but mostly not sadistic nobles, possibility of advancment on social ladder and there is no danger of me being enslaved.
I think i would prefer holiday in Orlais.
1. Lack of Rights vs. Privileges are two sides of the same coin. You can say a Chevalier has special privileges or you can say a serf has no right to complain. Same difference.
2. We've seen Tevinter parties in the comics and while Fenris was witness to some pretty gruesome stuff, the Tevinter parties by and large DON'T have that sort of craziness. Any more than, presumed Vaughn and his men "party" with the local elves was normal in Fereldan for noblemen. Danarius was an awful mage even by Tevinter standards.
3. Tevinter seems to have the highest technology and living standard in Thedas.
4. It's also the only reason the Blights have been defeated and since the Taint existed in the Deep Roads beforehand. It was only a matter of time before the Old Gods were tainted anyway. Indeed, it's very likely Dumat was already tainted since HE ARRANGED for the Black City ritual.
5. You can't advance in Orlais as there's no opportunity for social advancement in a hereditary military dictatorship. Ser Michel is an imposter who had to lie about his parentage to pass himself off as a chevalier. He also, I remind you, engaged in race-based murder as part of his initiation.
Either way, this kind of darkness is what I wanted from the portrayal of the lands and everything seemed softpedaled.
I wouldn't have MINDED Tevinter as the Red Wizards of Thay from Forgotten Realms (remember them from Baldur's Gate?) and it being Fantasy Mordor.
But it and Orlais were given the whitewash treatment.