I kind of wanted an actual excerpt of the fight, but okay ><
Where did the battle take place in? I can tell it's somewhere in deep space, but which universe? I'm guessing sword universe since they didn't seemed to have moved when they captured and subdued Narukana. The Time Tree does reside within sword universe, so...
Don't forget that Unmei is wielded by Rogas, so Unmei/Rogas being fairly stronger than either Narukana and Seii shouldn't be surprisingly. Higher eien shinkens are stronger when they're wielded since the user can bring out more of their power. This is especially true for an incarnations like Narukana and Seii.