I still think a scaled down version of the halo rings "Purge devices" Would be ideal. Could try and incorporate some lore into them, calling them the prototype phase of the halo rings designed to purge a nearby planet of all life. However once they realized the rate of the flood infection was far too great they had to upscale the design for much more.... devastating effects.
nope. When a picket force of forerunner cruisers can clear a system at the same rate, this kind of thing is too OP,
This is just an exhausted topic. We've considered a lot of possibilities, haven't decided upon one. Sternus is right in the case of the Halos being superweapons, and it's been said that superweapons aren't necessary for SotP because they are designed to break stalemates and it's a top design priority to prevent them in the first place. The most likely candidate seems to me to be the artifact world or whatever it's called in Rebellion, such that capturing a Halo is a victory condition. But who knows? We'll decide when the time comes.