Well, if that isn't the worst possible explanation, then I don't know what is. I never thought I would see a scene that makes me appreciate the Architect in Matrix: Reloaded, but, nevertheless, here I am. It truly is beyond my comprehension that the writers could have devised an explanation that clashes with everything established in the two previous games.
Whose bright idea was it to make a race of murderbots to protect the galaxy from a potential killbot rampage? And they accomplished this by programming the murderbots to rampage first, before the killbots are created? What? Drawing attention to this fact doesn't make it any less stupid, Bioware. Using this "ascension" nonsense doesn't change much either. Unless ascend means to fry with lasers or refers to huskification, it seems that Reapers don't ascend a whole lot of people. Sounds kind of like a killbot to me.
Why wasn't this Oracle, who was evidently stationed on the Citadel the entire time, programmed to send the mass relay signal to the keepers? Wouldn't that have made things a lot more efficient?