Again, what is your point? I never brought up Arlathan's social structure or how nice it may or may not have been to its own people. If you want want to call the elves a bunch of hypocrites for having a society of their own at some point in the past, I really don't care.
They killed people to live forever. That's the definition of a parasite. Saying, "How's that a parasite. They just used the Fade," is wrong. They didn't. They summoned demons and killed each other. As much or worse than Orlais. Parasites.
Just because someone says something doesn't mean its necessarily true or that he even fully understands it himself. We know for a fact the taint makes the dark spawn ageless. We know blood magic can be used to manage/cleanse the taint. We have very little direct evidence that blood magic grant immortality right out of the tin. And finally the 'blood' powers you get from him are all taint related.
I'm going to use the definition presented to me instead of your opinions, if you don't mind. We know the Taint doesn't sustain Grey Wardens. We know Avernus is a Grey Warden. He clearly states what he did. His opinion is above yours in every way.
All that said, its seem reasonable to draw the conclusion that the taint is what was keeping him alive, while blood magic only keep him from going full-ghoul.
Except it's not, by any stretch of the imagination besides your own words.
Your right it doesn't and yet the tevinter system has endured millenia. In all that time why is it no one seems to have even pushed say 200 years old? If the magisters are really supposed to be as powerful as they are portrayed and blood magic can do what you claim, surely a handful of them would be known to have lived beyond the means of normal human longevity. And yet no one has, I'm not asking for an invulnerable immortal, just someone who say managed to double his lifespan, given the system is stacked in their favour surely there would be at least a few of them no?
Your acting as if Tevinter isn't a cesspit or corruption, persecution, slavery, and duels in the streets. These things happen all the time. And yet Tevinter goes on. But you know, the elves had powerful magic, so they didn't do these things and really lived forever. Do you honestly believe elven dreamers would be the only ones to discover such things?
Not necessarily, considering he's the only example we have, nor do we know exactly how the elven fade-siphoning worked before.
Um, what? If the Fade was keeping him alive, why would he die instantly from releasing the curse? No spirit has ever been able to sustain anything before, even Justice using his body until it became a rotting corpse. Much more than it was before.
Similarly the argument can be turned on its head, if a blood magic spell was keeping Zathrian hale and hearty all this time, why would he suddenly die if it stopped? Wouldn't he just start aging again like a normal elf, after all the spell essentially hit the pause button on his aging process, why the instant death?
In my opinion, which doesn't contradict things said in game because I believe that they make no sense to me, Zathrian bound himself the spell he cast. Well that's sort of my opinion, but mostly what was said in game.