Dragon age thoughts...
I'm replaying dai and I'm getting the vibe that Andruil might have been the one to create the blight.
Reason one: when you talk to Solas about the grey wardens and their plan to find the old gods and kill them before they could start a blight... He is just so unbothered by the IDEA of the blight that it's just not something you would go to that extreme over.
Reason two: Andruil went to the void and fought "forgotten ones" and got sick in the head over it. Mythal had to stop her and take the "knowledge of how to get to the void" out of her brain
Reason three: That makes me wonder if Mythal/Flemeth know how to deal with/not get the blight. She rescued the grey wardens out of a dark spawn filled tower... She lived in the kokari wilds, where the blight started, where the dark spawn were swarming. The dark spawn that poison and blight anything they're even near.
Reason four: here we get to my wild supposings... The eluvians and access to the crossroads were turned off following a war between the elves so enemies could not get to them (as stated by a morrigan who drank the well and did not have keiran)... There is also a codex entry where if the inquisitor drinks the well talking about the elves at the temple of mythal. It says they are "trapped" (probably when Solas erected the veil) and "the ones born here do not understand the keeness" of what they have lost, or "why so many elders weep as they enter uthenera." What if the ancient elves had like... Tons of little pocket dimensions right? Accessible thru elluvian. I'm assuming bc, when you go with morrigan the to the crossroads the gate you come out of has like little statues on either side of each elluvian. What if the elven gods all had their own little pocket dimensions? And the black city is Andruil's bc ........ She also has this entry where her followers were begging her not to use a big ol weapon on them. What if it was the blight? Or an anti blight weapon? But! What if the magisters entered the fade and went to like a quarantine zone (bc they say they tried going to the golden city and it was empty). What if it was blighted, they got blighted and brought it back to the "real" world?