The same way if he wrote jellal vs laxus they'd still be equal. You think Hiro ever going to write a fight where Erza laxus and Mira beat jellal? Lmao think again.
Natsu and gray will never be equals. Hiro murdered that rivalry when he introduced suzaku. DF natsu eviscerate gray it wouldn't even be a low diff, he gives Erza that treatment to. This MFS aren't even hyped up to be world ender like natsu.
@Ronin31 no way in hell even you believe gray=natsu. He doesn't have the feats to back this up. Same with erza she simply doesn't have the feats to back up why she wins. If you have panels from the manga that shows it post it