You're not actually talking about the relic, you're talking about round #3, where any non-MC, non-IC unit could take it and reap double kill points.
Look, you have weird, "cinematic" missions with odd rules, odd niche situations will occur.
I'll argue that having a thunderfire use the "bit O'emperor's armor is less weird than Mephiston being able to....He is neither an MC nor an IC but he is very close to being both.