“Mikasa was quick, powerful and certainly experienced, but Blake’s versatile semblance and powerful aura let her steal the end to this fight.”
“Man, Mikasa sure found herself in a cat-astrophe of titanic proportions!”
“The winner is Blake Belladonna.”
You can already hear Wiz and Boomstick declaring Blake the victor in your head. It’s pretty obvious why – Blake is a super-powered Faunus with Aura, Semblance and Dust, while Mikasa is just a person. No tricks, quirks or supernatural abilities. The only thing she can do while Blake is beating her senseless is to get emotional for a bit.
Blake has been shown to be a formidable duelist in any range, owing to her incredibly versatile Gambol Shroud. Meanwhile Mikasa can fly up really high in the air… Sure, it might be a different story if it was a Titan-slaying contest (and even then, Blake did fight a 500 ft. long lightning-breathing dragon!), but Blake is a Faunus huntress, not a freaky giant. Most of Mikasa’s skills and equipment aren’t really that useful in a fight against a small, mobile target.
As far as defensive qualities go – the battle’s decided right there and then. Blake’s aura can withstand force that would be lethal to a normal human without a scratch. Mikasa doesn’t have that luxury, meaning a single shot from Gambol Shroud could end the fight instantly. It might even end before it had a chance to start if Blake attacked at night, since her Faunus eyesight and hearing grant her superior perception.
Finally, let’s not forget… the biases. DEATH BATTLE! is owned by Rooster Teeth and RWBY is one of their most valuable properties. It’s easy to see how higher ups at RT (or even AT&T) could demand a victory for Blake just to raise awareness of the brand. There’s been precedent before, just ask Tifa.