Also, remember the story about Andruil and the Void?
The way it is described reminds me of the taint and the blight - driving gods mad, plaguing the lands, the true darkness meant to be forgotten. What if it is the taint? Somehow it filled the Golden City=Arlathan and then the magisters
My own personal belief is exactly that. I believe that the Taint stems from that area of The Void, and in moving Arlathan to it Fen'Harel would have (probably unintentionally) forced the Elven Gods to be twisted into new and darker forms.
Yes, we are told that the Blight began with the Magisters, and that it was The Maker who cast them from the City transformed into Darkspawn. As a punishment.
But what if, actually, the tainted Elven Gods called out to the Magisters in an attempt to be broken out of their prison. And merely coming into contact with them resulted in the same Taint (which was native to The Void) infecting the Magisters as they arrived.