Actually your argument works the other way around.
Also, I don't get the whole idea of them spreading outside the galaxy, since the games state they go into dark space to hibernate (I get that some people just don't get that "dark space" isn't some corridor between galaxies, but that the distance between galaxies are unfathomable), to conserve energy between harvests. They are not advanced enough to fly to another galaxy. ALSO, they are not programmed to.
Dark space is not a corridor...who said that? They live outside of our galaxy.... I have no idea where you get this. And you say that the distance between galaxies is "unfathomable" but in a billion years they can't doit but we can in the midst of a war where we are starving for resources and throwing everything into making the super weapon. Right, makes sense.
As far as programming, we know that is meaningless, because they have already violated their original programming.
Hibernation is a cop out. The wiki says that, but it also says they hibernate for 50k years at a time. If you carefully play ME1, you will learn that there is no 50k year cycle, but that they return when the time is right for them to show up to save organics from some synthetic menace. It was later that they turned it into a 50k year cycle and that they hibernate in the meantime to handwave away any real answer there. The lore here is inconsistent. Besides a 50k year cycle makes no sense, since by the time they wake up to reap, all the organics might have been killed by synthetics. The idea at first was that they monitor the situation somehow, presumably via the Citadel. This was implied, but never clarified, though it was suggested at the time that those critters on the Citadel that ran around repairing and maintaining it were the ones doing the monitoring. There was a lot of missed opportunity story wise there, by the way.
So no, sorry, it makes no sense. The story, the lore, all of it is inconsistent. There are several loose threads, false starts, dead end plotlines in the whole thing. It is some of the sloppiest most incompetent writing in all of fiction.