User blog comment:FairyRaven/Fairy Tail Chapter 398: The Final Duels, Review and Commentary/@comment-7418318-20140901145939/@comment-5268982-20140901200145

As others pointed out, the thing is that Natsu and Erza always one-shot their enemies to oblivion by raw strength that sometimes has a questionable source(aka their feelings or Erza's samurarmor) while Gray always uses his wits to get shit done(Lucy as well). That's why it's acceptable for Gray to one-shot an enemy to my eyes. Besides, I think Mashima builds it up to show us that he's equal to Natsu in case they fight in the future.

As for Lucy, I loved her fight and her victory was most definitely deserved, so I disagree with each and every one hating her victory(-ies) ;D