@Selaphiel  
I totally agree, although Sunset definitely fits the niche of having a complicated mother daughter relationship with the ruler of the kingdom that led to a big falling out. That and their love for punk/black leather clothing, like how Sisigou summoned Mordred because she was the closest in personality.
 
While Rainbow Dash would definitely fit Mordred in personality, an alternative I’ve heard brought up is Cu, as both of them, RD and Cu, are free spirited, competitive, speed and strength focused heroes who are total bros that love their alcohol when relaxing.

Whoa sunset looks all kinds of badass

Well sunset shimmer just ruined my favorite character.

I feel Rainbow is more in character with Mordred. While Sunset would have been Scathach.  
But this is beautiful too.

Sweet loving sunlight o.O