If it's hyperbole, it's not far off. Remember, we're not working with just two life cycles here. They've been successful for millions of years.
Quite a bit far off...
Lets say they've been at it for 2,2 billion years. Building a new reaper every 50.000 years (not every circle and maybe more than one in others). Thats only 44.000 reapers or smaller cuttlefish.
Enough to pretty much deny any hope for a victory through conventional weaponry, but far from enough to "darken the sky of every world"... There's an estimated 50 billion planets in our galaxy.
But threatening aeronautical display on every planet they wanted to reap? Sure...
Personally I prefer the future setting, get rid of the silly reapers and find me some saucy future interspecies intrigue... where anything can happen.