Have you seen this idea published anywhere?
I actually don't remember reading this anywhere, it just seemed an obvious idea. The idea that humanity would expand into a Type III civilization and near light speed is very old, probably dating to the work done by the British Interplanetary Society on interstellar travel. I don't have citations handy, but I remember reading a critique of generation ships which basically boiled down to "if you travel less than 0.9c, you can expect someone else to leave after you do but arrive sooner." Applying the same logic to other civilizations just seemed like common sense...
Full disclosure, my brother is the author of the first book.
The probability that a new civilization is born after the light from the expanding one has arrived, but before their colony ships have, is very small, so therefore we should expect that whenever our civilization was born and whatever the benevolence of the aliens, when we look into the sky we should see no sign of them.
When you are making assumptions about the millions of civilizations, it is absurd to think they ALL retreated to playing video games for eternity, or ALL nuked themselves to oblivion.
With a single super-predator civ, that has a huge leg up on everyone else, they can have unusual motivations, and techniques. The problem with a super-predator is you likely won't be able to learn anything to prove or disprove them until you meet them, with all that implies.
I am not making this up, but I may have dreamt it!