User blog comment:SethHeartphilia/Whos stronger Erza or Mirajane/@comment-26461051-20150607045403/@comment-26461051-20150612002321

If Mira's darkness can break Erza's armour, than she can just dodge Mira's attacks with her flight armour, or black wing armour. I might be mistaken, but Mirajane has never really shown any major defensive feats before; sure, her satan souls make her more durable than she is as a normal human being, but Mira has never actually taken the kinds of hits that Erza has taken.

Yes, I know that Mira's attacks have more raw magical power behind them, I said myself that offence is clearly Mirajane's specialty. As for reflexes, Erza and Mirajane have both displayed amazing amounts, I think that their reflexes are almost equally good...

So yes, Mira's attacks have more raw power and speed (and they look really cool, too), but the sheer variety of Erza's magic and attacks (I explained this already in my above comment), her ability to make strategic split-second decisions, and her skill with weaponry even things up.

In other words, they are BOTH awesome, just in different ways...