User blog comment:IamJakuhoRaikoben/Chapter 492: Elder Sister and Younger Sister, Review./@comment-25111584-20160704162214/@comment-3290324-20160704175801

No, you’re just looking at it the wrong way. In addition to what you mentioned, we got the intrigue of getting a new Satan Soul (a copy of an extremely powerful Demon btw) as well as the knowledge the Mirajane probably absorbed other members of Tartarus. Which is more than enough information and pizazz for a fight that lasted less than one chapter.

And Mira losing here would’ve been terrible writing and completely nonsensical. Juliet and Heine were not major characters or threats and Mirajane losing to them would’ve made her look weak and it wouldn’t move the plot forward in any major way. Mashima would’ve simply upset fans pointlessly. And would the fight have been better for fans if it was longer? Of course, but it makes sense for it to be shorter. Magic Power replenishes. So even if she did exhaust herself a bit, it wouldn’t have put her down for the count. And finishing those two as quickly as possible was in her best interest. You don’t spend a long time facing foot soldiers when you’ve been told that not only your friend, but the one thing that can end the entire war and possibly the world (Fairy Heart) is in danger. That’s just ridiculous.