Why is it so hard to imagine the Sathanus fleet is simply still, just the tip of the iceberg?
What does it have to do with this topic ?
Odd though how fast the Shivans could have descended upon their homeworld.
Simply; The Shivans have a track record of only deploying resources required to destroy a specie, not overkill a specie, and since the Ancients were such a huge chunk of empire, it's quite likely they saw things we never did.
They also never ever faced an equal opponent, never faced a losing battle, never fought a superior opponent, their 'arms race' was probably quite slow, as was their ability to shift tactically (not that GTVA is as fast as I would like, but certainly I imagine them being significantly better than an empire that spans multiple galaxies).
Fubar; I kinda agree but reachable is very vague, that could mean however many lightyears = their lifespan or more, or less, that could mean their local cluster, or their spiral arm, or their entire galaxy.
No way to really tell, but certainly I can't say you're wrong in the slightest.