Nobody has been nerfed. Period. A real nerf would be like Thor getting fat in Endgame when he almost killed Thanos in Infinity War. Or in Fairy Tail, like when Makarov started having health issues or Laxus getting poisoned.
Natsu beating Gajeel is a more impressive feat than beating Jacob or Neinhart, because Gajeel can kill Bloodman. Beating someone that can kill a Spriggan is more impressive than simply beating a Spriggan. Bloodman isn't a warlock.... I don't even know what that means. Bloodman even throws melee attacks. Gajeel said that Bloodman's magic power is the lowest out of the Spriggan 12 because it is. Bloodman uses curse power, and he has Spriggan level curse power
Lucy wasn't even serious injured against Jacob after being hit like 20 times. Levy wasn't hit by Natsu even once. He couldn't muster up the will to actually punch her because she was pregnant.
Mirajane and Elfman didn't deal more damage to Bloodman than FDK Natsu. Madmole was barely scratched against Mirajane and Elfman. FDK Purgatory actually managed to knock Madmole off his feet and seriously damage Madmole. It was impressive enough for Skullion to order a retreat.
Makarov had more magic power than Wraith. The Spriggans probably have more magic power than Wraith too. Despite having all of that MP, Jacob's attack power still sucks. If the Alvarez arc has taught us anything, it's that having higher MP is meaningless unless it actually translates into something useful.
Ignia's flames dragonized Natsu were hot enough to burn his own arms. Overpowering Mercphobia's serious roar and burning away all of Mercphobia's remaining magic power for the rest of his life is more impressive than setting the ground on fire....which has never actually been impressive. Natsu literally used Mercphobia to smash the city, so I dunno what you are on about when you say the environment was untouched.