And, The Architect all but said he was an anomaly - a darkspawn who awoke to self-awareness with no explanation of why it happened.
I realize that one takes the word of any character at their own risk: that character may be lying, may be omitting details, or may honestly not know the truth. However, that does give context to why the audience may not equate the The Architect to the Tevinter Magisters. Especially when, as you say, The Architect is just one of several talking darkspawn in Awakening. That he has a unique character model means nothing. The Mother also had one.
The Architect didn't know of his origins though, he was merely theorising... or perhaps he was just flat out lying, we honestly don't know?
In the course of Awakening we learn that he had already omitted the truth once already, by not admitting that he was the one who started the Fifth Blight in the first place when he attempted to awaken Urthemiel, believing that telling the Warden that would mean they'd refuse to help him.
You could imagine that if he does remember who he actually is, why he might not want to tell us that instead of causing one Blight, he accidentally helped (indirectly) to cause all of them?
As for why he's one of many talking darkspawn, that's because he was the "first" and used his blood to help create the ritual that gave them sapience. The Calling novel shows that he existed long before Awakening and makes no mention of other talking 'spawn (since his plan was different back then), so they had to have come from him as part of his new plan?
It would also makes sense that if he is indeed one of the Magisters who first served as the progenitors of the darkspawn, why he's such an anomaly and why his blood would have special properties that would prevent the Awakened 'spawn from hearing the call of the Old Gods?
That's also probably the real reason why Archdemons get destroyed trying to jump into a Warden, as the presence of the Archdemon blood in both parties somehow cancels each other out. Hence why Corypheus can jump into another Warden with no problem, since he doesn't carry Archdemon blood within him, (Warden bodies probably don't carry enough to affect each other, hence why one dying doesn't kill the guy next to them, so Corypheus can survive the process even while using a Warden host), as well as how the Archdemon can jump into nearby Darkspawn who lack that same blood-type. The whole "soul" explanation is actually false.
The Awakened being self-aware and free from the Calling could be the result of having three different blood-types inside them (and perhaps versions of the taint), the regular stuff that all Darkspawn carry, that carried by the Progenitors (Magisters such as the Achitect and Corypheus) and Archdemon blood (carried by the Wardens).