Actually not that circular, imho.
I see it like this, Vasudans, Humans, Ancients crossed into subspace and went waging wars around, Shivans decided to kill them, they did so with the Ancients (as far as we know
), failed at the Humans and Vasudans because of an unexpected alliance, they then decided to cause a civil war to weaken them and moved a Juggernaut fleet into Capella to use it as a time, dimensional or whatever jump to keep them in reserve for the inevitable strike, Vishnans however, were intrigued by the development of Ubuntu in Sol and the philosophical transformation of the Vasudans without the corruption from the Parliament, and thought that, maybe, they could be worth keeping around, but the Terran half of the GTVA had to be converted or eliminated, now that the UEF is starting to fall to the dark side and the Vasudans allowed themselves to be dragged into the war, they might have changed their minds about the whole thing, and might let the Shivans wipe their slates clean, since it's clear that the Terran GTVA is as a corrosive force as the Ancients were.
The words "the creators blundered once and in doing so unleashed the the deepness that now stalks the cold roads" seem to imply that the Brhamas hesitated and bought ruin as a result, "they burnt the cosmos clean in the wars of their youth" possibly a reference to the ancients, which forced the Brahmas to create the Shivans and Vishnans as guardians for those who could not fight back and prevent a new multi-galactic empire from being even dreamed of. "Never again will that price be paid" they are not willing to take any more chances, as they took enough under the Vishnans' insistence.
So the Shivans are simply being cautious, they won't risk another wildfire across the universe.