The halo rings explicitly ignore space and time. At the end of Halo silentium, omega halo was used against the flood, and the wave instantly wiped out a nearby galaxy. They ignore space and time so hard, the forerunners were getting reports of a successful firing of the array, before they actually fired the array. Of course you're also assuming that for this debate the Star Wars galaxy and the halo galaxy are millions of light-years apart. If that's the case, the only side that can go on the offensive is halo, because the precursors, forerunners, and flood are the only race that can travel intergalactically at a reliable speed.