User blog comment:FairyRaven/Fairy Tail Chapter 349: The Demon Doriate, Review and Commentary/@comment-4938779-20130830193055/@comment-1776824-20130830212154

Erza beat Kagura because:
 * 1) Friendship pants
 * 2) Kagura gave up

Erza beat Minerva because:
 * 1) Universal-distorting armor

All in all, they're rather even in strength, imo, it's just that Minerva couldn't use her Magic because it was getting sliced into pieces.