AWESOME theory by the way. But lets put some things in light.
Awakening does show several facts about the black city. Things in the real world are not the only things that the fade can show. And from what I remember it shows what PEOPLE felt, dream and think about. not places per se. I may be wrong tho. The magisters and DA:A shows that its possible to enter the fade physically I mean thats what this whole DA: I is about.
Also, Solas, the old elves of the temple of mythal told us many things: The magisters, Tevinter, the humans arent the one in cause of the DESTRUCTION of arlanthan. that were his words. he said they themselves did that. So in one side we talk destruction, not a still fully built city. On the other hand, He said directly that the humans were not in cause.
Many other factors comes in aswell: Fact that David gaider said the elven lore is mostly inaccurate, since they are remnant of pieces gathered together and interpreted. Solas and the Old elven guardian mentioned that the Dread wolf did not deal the old gods like that, if at all. Its also mentioned that he looks out after his people (according to him) and he is also friend with an elven god. We dont know if there is only one hes friend with, what else we dont know, why was he in slumber etc..
Also the Old God arent already tainted when they are found. they are found to be tainted. The architect says also that HE TRIED to make Urthmiel a disciple but it made it an archdemon instead.
I like also you recongnize the two things The elder one says about the black city being already black and golden later one. We also know nothin of the fade pre blight. The dreamers, why Tevinter believed in Andreste later on. (the reason why the magisters went there in the first place) Corypheus said he DID see a throne, and that there is power there.
Later on a found a new codex entry that talks about a city completely disapearing (including a huge chunk of ground) There was also other stuff about it, sounds like black city to me.