The hints were always there
I'm still playing through the Veilguard, but when it comes to the lore and possible retcons I feel like I have a vastly different stance than other people. I saw people being displeased and saying that DAV did ignore the canon or devs forgot about the established canon (which may have happened with so many revisions to this game, not gonna lie), but to me it's a case by case basis and so far I have no complaints (but admittedly I didn't finish the game yet, so it may still change).
For example: the entire thing with changed properties of the Blight is a sign that rules of the Blight within the world also changed. The game goes about it roughtly like this "long time ago Blight was even more nasty and bad than it's now, then Solas sealed it in the Fade that got separated from the mortal world, so when the Magisters entered the Black City and released some of it, it entered a vastly different world where there were no Fade and no Elven Gods". Which to me implies that the state of the world post-Veil and the fact that the Elven Gods were no longer in it affected the Blight. The world in which the Blight was born was long gone so it adapted accordingly. It became more passive despite still being operational, and got linked to the presence of the Archdemons (i.e. Blight exists, but doesn't happen on the larger scale unless there is a blighted Old God leading the charge (except of course underground where dwarves are battling it constantly). It found new ways to create the Darkspawn etc. because it was forced to do so to continue operating despite being cut from the source of its power.
Therefore it's not weird to me that all of the possible cures to the taint / Blight / the Calling talked about in the previous games / media aren't applicable in Veilguard anymore. Ofc they aren't. Blight is no longer a sickness in state of semi-active dormancy. It's no longer passive as it used to be. It's at full "fuck remission, imma strike again" stage doing whatever the hell it wants. You can't cure it with the old methods you knew anymore. You have to first improve the cures you found before in order to have a shot or beat the stronger virus now at all. So expecting all this old lore to be somehow relevant still seems excessive. Albeit I wouldn't say no to the game actually openly saying "we tried all those methods and each failed, this new Blight can't be cured by them".
TBF it seems that the hint that Elven Gods were always connected to the Blight was right there since the very beginning in DA: Origins already, otherwise the Old Gods wouldn't be so important for the Blights to happen. We just simply didn't know that the Old Gods and Evanuris were connected, even though for years we theorised they were connected in some way, if not one and the same. To my knowledge nobody ever proposed an idea that the Old Gods were basically glorified pets / war hounds for the tyranical elven gods. We were right tho that they were one and the same, as the dragons were their connection - speakers for the imprisoned Elven Gods.
In Veilguard it's very much implied during Solas' memories that all of the new Darkspawn we meet in DAV are in fact not new but just old. They simply had no way of existing without Fade World and the Elven Gods in the world, but now with the Veil weakening and two of the Elven Gods released upon this world via a powerful magical ritual that possibly weakened the Veil even more, Blight could finally become active in a way it wasn't for thousands of years. The same logic was also applied to elven artifacts that Veil Jumpers are dealing with in Arlathan forest. The ritual that Solas did and the releasing of the Elven Gods, it all affected the world in ways nobody knew it could before. Nobody knew how important or connected to the world Gods were or how powerful they truly were. As primordial spirits turned first people of the elven kind, they have far more intrinsic connection to and understanding of the world than any other race, except the dwarves so far (as dwarves turned out to truly be the children of the Titans that were actually the first inhabitants of Thedas as far as we know now). We don't know yet how humans and the Qunari factor in this (albeit I have some theories about the Qunari - in short they could have been created as soldiers / slaves that were supposed to be immune to the Blight thanks to the dragon blood they inherited, but it turned out they weren't and hence why they're referred to as a "mistake" or "beast of strange blood" with a "blood engorged with decay" (Corypheus) or having a "blood that doesn't belong to their people" (Kieran)) but it's undeniably true that elves and dwarves are connected to the world of Thedas in ways breaching human understanding. So it's not weird that world went wack when just two of the Elven Gods came back on top on Veil weakening and Titans already waking up in Inquisition.
I know what you will all say. "But what about Solas or Mythal?"
Mythal doesn't count, because she never managed to get back her true form and kept existing in a state that is very similar to Anders' case of spirit + human merging. Solas doesn't count as he was asleep for thousands of years and when he woke up he was not even able to use any of the artifacts due to losing his powers (hence why he needed to consume Mythal's essence / soul). On top on that he also wasn't Blighted. He only counts as far as his ritual goes because it did wack to the world. (It fortunately didn't release more Blight, but did use shitton of magic that must have impacted the world where Veil was weakening all over already).
Not to mention how many things suddenly make sense.
Mirror in Mahariel's Origins being Blighted and Tamlen seeing a "great blackness" in it confirms that Ghilan'nain was connected to the Blight, as it was her mirror that Tamlen and Mahariel find - in DA2 it specifically has a symbol of a Halla on it to highlight it.
Dwarves not having dreams and being the only race that can't perform magic but also being able to perform it when they're born as Genlock Emissaries, mages in general getting magic power from the World of Dreams but when they're made tranquil loosing that ability and their dreams with it as well as the elves becoming magicless in the world where dreams and reality no longer coexist is all an expression and a result of Blight being created by the actions of the elves in the Elven-Dwarven war and by the creation of the Veil afterwards. (Like seriously it never struck me so much as it did when I played DAV - before I was like "oh yeah magic comes from the Fade" completely forgeting it's the dream realm that souls visit in dreams and go to after death).
The fact that the Blight song is always driving the Darkspawn to seek the closest Old God in order to blight it and take charge of the army of Darkspawn that otherwise is aimless without anyone to lead it. Blight probably designated them due to their link to the Elven Gods and used them as proxy in place of the missing gods because it was already accustomed to being used by Evanuris in their wars, hence why Darkspawn need Archdemon for the Blight to happen - they can't invade the surface without a commander.
There is probably more of those stuff.
The more I keep thinking about it the more I feel like this:
It was all just THERE. All. This. Time. In plain fucking sight. But we didn't get it, because we lacked the necessary contexts to get it all!
We thought that the Blight was only connected to the Titans, but we also knew before that the Elven Gods were possibly blighted thanks to what happened to Corypheus and other Magisters Sidereal. We just didn't connect the dots that Blight may albo have been used by the Elven Gods in similar way Corypheus used it. Hell, it's so ironic that in some theories we considered a Blight an immune system reaction of the body to the invading viruses and now it turned out that the Elven Gods - the ones that were considered the first invaders by the Titans, became their tool to spread the Blight (even tho they think they lead it as all powerful rulers it's very much possible they're just useful idiots). It doesn't matter that the Evanuris were the ones who actually created the Blight while seeking more power (via Titans' souls), what matters is that it was all connected and Blight was punishment meant for THEM.
The fact is they destroyed their own Empire with this blighted power, no matter how much they gloat about how powerful they've become.
No matter what they say, Titans' dreams have already won.