So, you actually agree with me: Kagura lost (partially) because she didn't have the will to fight and win.
Kagura isn't a protagonist. All the will to win in the world wouldn't have allowed her to beat Erza.
Originally Posted by Kraco
Erza also doesn't always win. She couldn't win against Jellal, for example, and needed Natsu to save her. Obviously she didn't have the will to win against Jellal in particular.
Because that arc was better written than this one.