True , I just think we need more information too make a real judgement.
We need more information to get the complete picture, true. But so far, we can make a judgment: that the Chantry's version, embellished and extremely biased as it is, it's the one that gets more sources backing it. Including the important part about Magisters + Fade Walk + Darkspawn being related in some way or another. That's the real matter here, because it's the most important reason the Chantry uses to speak ill of mages.
That the city was golden or black before or after the Fade Walk, that the Maker spoke or not, that Dumat tricked them or not is secondary and looks more like an attempt to avoid adressing the main issue here: that a Tevinter Magister did perform a Fade Walk to try to reach the fabled city and that he became tainted and was part of the first darkspawn known by Thedas.