No. The line saying they're stronger than before simply debunks any nonsense about any members of Fairy Tail being inexplicably nerfed for no apparent reasons. Natsu's feats in the sequel is above what he did in the Alvarez arc because he's beating up more impressive opponents:
- Gajeel killed Bloodman during Alvarez. Natsu beat Gajeel using LFD, and had energy left over to beat Makarov. It should be a no brainer that beating Gajeel in hand to hand combat is more impressive than beating Jacob.
- Madmole tanked shots from both Natsu and Mirajane that would have oneshotted Jacob. Natsu overpowered Madmole with FDK Purgatory.
- Even beating up Makarov is more impressive than beating Jacob or Neinhart. Makarov smashed Jacob with a punch, and tanked the Jupiter canon with an arm. Compare this to Ajeel getting wrecked when he was hit by Jupiter.
- Natsu with Ignia's flames is more impressive than Natsu with Igneel's magic power or raging flames of emotion.
The only thing Natsu has done that is more impressive in the Alvarez arc than the 100YQ is beat Acnologia. And that was done with the help with all 7 dragon slayers and Fairy Sphere severely weakening Acno.
Also, the size of Natsu's attacks does not matter. What matters is how much damage they do, and the durability of his opponents. The attack that beat Zeref was room sized. The attack that beat Acnologai was building sized. The attack that beat Mercphobia, who was stronger than any of the Spriggans, didn't even produce a large onscreen explosion.
It's actually prove main characters (some of them) was nerfed for plot issues, because they became to strong for any participation in further events.
FT has more then 500 chapters, but BS about "Natsu magic is not working underwater" we saw only in sequel.
Skullion was not able to turn Wendy wind into "ash", so his "turning to ash" with water - strange and unexplained. His "fight" with Gray was like in cheap Chinese web novel with Marty Sue.
About your marks.
1. Natsu was stronger then Gajeel since Phantom Lord arc. Natsu beat him before w.o. LFD modes. Yeah, Gajeel stronger then he has in PL arc, as well as Natsu. But why we suggest Natsu vs Gajeel should mean anything ?!
Well, it should, because actually against FT members - Natsu gank used far more power then these DE. It's true. Entire first "battle" of team Natsu vs DE was a farce.
1.1. Bloodman is not melee fighter (he's warlock, he used curses). Gajeel stayed himself Bloodman magic power is lowest from all S12.
So with base on what you got idea defeat Bloodman for Gajeel is more impressive then for Natsu defeat Jacob ? And how one and second are correspond ?!
If someone want say again how Lucy didnt die in battle Jacob vs Natsu... well Levy as well didnt damaged in battle Natsu vs Gajeel.
(as add: Gajeel effectively died himself aganst Bloodman and was saved with plot armour).
2. Do that guy should be tank as armour DS ?
Well, basic attacks of Mirajanne and Elfman dealt for him more damage then FDK Natsu.
You will say it's not nerf for Natsu ? If Natsu FDK looks weaker then basic punches by Elfman and Mira....
3. I believed Macarov himself stated how S12 strong and how impossible to beat them, If ikr his magic power lower then S12.
When Wraith meet Macarov - Wraith has shocked how much magic power that dude has.
Is it joke or... ? If DE shocked by Macarov magic power.... compare them with S12 is pointless.
4. It's out of logic, sorry. Igneel is King of flame dragons, He's top tier dragon and Acno recognised him as worth enemy.
Ignia as cocky chicken who run and hide with fear of Acnologia. He confirmed it himself.
When Natsu used remainings of Igneel flames - it was able to melt to nothingness all, include earth, and Natsu was in clear mind. With Ignia flames (when Natsu was out of control, and wasn't properly control himself) - environment like buildings, trees etc was untouched.