Yea i get its got defenses an what not but also: A hollow large object is MORE fragile than a solid one. A sphere is the strongest geometric shape. If the halo's orbit decays an the gravity of the gas giant it is orbiting applies torsion in just the right way; the ring can snap Halo is 2/3 the diameter of EARTH death star is smaller than earths moon Halo is far more susceptible to torsion and torque the death star isnt.