But if you take 1 billion years as the low end of the age of the cycles, you still get tens of thousands of Reapers: 20,000 Sovereigns +100,000 or so destroyers and support ships.
Which is just stupid given the entire galaxy should have fallen pretty much instantly to that kind of power. With plenty left over to go exploring other galaxies even without machine servants.
Sorry, it's still not "legion" enough to "darken the skies of every world" in the galaxy... which is what Sovereign claims during Virmire... or "legion" when compared with a organic populations that number in the trillions (as stated by Saphyria in ME1) - "When you represent trillions of citizens things tend to get a little busy." Keep in mind that the idea of being "legion" is based on numbers, not sizes.
Another possiblity is that each Reaper still considers itself to be "many" in number rather than a singular entity... but this idea is countered by statements from Reapers that are in the first person singular - e.g. "I am Sovereign."
Again, my point is the Bioware's writing has been extremely inconsistent. People are going to find "evidence" in the game in all directions - both for and against whatever "point" they choose to argue. That being the case, is any of the "lore" worth getting "married to." I say, let Bioware throw away whatever of it they want; allow them the "wiggle room" to hopefully construct a better, more consistent Mass Effect lore this time around.
BTW, are people forgetting that the Citadel itself was presented as being an "enormous mass relay that connects to dark space." (that is, the Citadel itself is supposed to be what makes the Reapers capable of "extra-galactic" travel (i.e. travel outside the Milky Way Galaxy)?... and the Milky Way species have access to that knowledge/tech at the end of ME1 (through Vigil's data file).