I've been meaning to address this.
We've established that the True Humans are...inhumanly efficient at converting a world populated by other intelligent life to one dominated by their offspring. Should they encounter one inhabited by hostile life, whether intelligent or not, they would be capable of rapidly asserting dominance using their innate magical abilities. The very epitome of a precursor race, immensely powerful but inevitably vanishing to leave behind their legacy for a later civilization.
So, where the heck did they come from in the first place?
Sit back and listen carefully, because I am about to BLOW YOUR MINDS.
Hypothesis: True Humans are aliens. At least, in the sense that they did not originally inhabit Earth.
To be more accurate, they are not so much aliens as a biologically engineered tool created by an earlier race.
Consider the characteristics of the True Humans listed above. They are pretty much tailored for one purpose alone: colonize a planet, secure dominance, and create a human race that eventually replaces them.
What if humans didn't originate on this planet, as we thought?
What if somewhere out there in the universe, long ago, far back before anyone can imagine, there was another, far more advanced, human race?
What if this race, for whatever reason, deemed it necessary to colonize other worlds in the universe? Spurred to do so by some imminent apocalyptic event, perhaps? Or maybe they were just a dying race, old and decrepit from having existed far beyond their time?
But in the nigh-infinite cosmos, there are precious few worlds capable of supporting life. And fully terraforming a lifeless planet was still far beyond the reach of the original humans, even after they had pioneered the art of space travel, though still limited by the speed of light.
So, what did they do?