I am gonna try and analyze this from a science perspective.
The rings all rotate in either a stable or a geosynchronous orbit. This rotation causes energy from various sources (light, friction, gravity etc.) to build and store, using the ring's own momentum to power it (think about it: an object that has achieved 100% efficiency and then some) and still have enough energy to store away for whenever the ring is activated/fired. As rotation continues, say the ring gets activated. The rotation should continue, allowing the energy to coalesce and spin in the direct center: multiple outlets and several ports shooting condensed blackened-plasma into a solitary point as big as the head of a needle. They collide, but the plasma has used up much of it's collateral energies in the clash.
What you have left is a different form of energy that hasn't really got an actual name - so we'll call it an Eldrich energy - that expands for lightyears out in every direction. This energy has afrequency and level of cohesion so high that it literally splits all carbon based life forms apart, dissecting them by the very atom to their most base components, then stripping off all electron particles the atoms contain - just dust and echoes as Cortana would say.
Case in point: Without said rotation, completion, callibration that the ring would have inevitably recieved and time to process and transpire a fully functional charge, the discharge that you are left with was not sufficient enough to destroy matter that wasn't in the immediate vicinity. The Ark? it's wiped. The Dawn? Not really. At the distance they were at, the pulse and waves of colliding energies would have made the *** rattle worse than a ghetto street car in a tourny, but it wouldn't have destroyed it or the beings on it. It just didn't have the capability yet.
When cities burn and armies turn and flee in disarray,
Cowards will cry "tis best to fly and fight another day."
But warriors know it, in their marrow when they die and fall:
It is better to have fought and lost then ne'er have fought at all.