But if that doesn't happen soonish, it will remain not-that-great, because we'll have leveled past the point where armies are a real threat. We're already damn tanky, starshine is anti-army, and celestial severance is/will become a "fuck that general region" attack. Sure, Supremacy Zone is nice, and does some good stuff, but it doesn't really define our play style like Indistructable Core does. If anything, I'd say Segarite Core has more right to be called our second super ability. Even without the insane synergy with Indistructable Core, 75% healing per turn is pretty good. Hell, Core Connection, which isn't even listed as one of our abilities, has done way more to shape the gameplay, not to mention the story.
So what I'm saying is: Supremacy Zone is too irrelevant to be a good super ability, and too weak to make itself relevant.