I just read the latest chapter. I have decided on my verdict on whether Laxus would have oneshotted Ajeel or not. My verdict is
NO , he would not have possibly oneshotted him at all.
Now we know Erza is capable of going against Red Lightning just fine. Even though she lost the match , she was more than a match for Laxus , she tanked his Red Lightning attack too. And the relative power levels haven't changed much since Alvarez arc. Nobody has got a mega powerup of sorts that skyrocketed their strength. It's ok to scale them to Alvarez.
For starters , this was Erza's condition after she fought Ajeel :
https://www.mangapanda.com/fairy-tail/459/7
Now , we know Ajeel is capable of tanking Base Natsu's punches just fine ( unlike Neinhart ) :
https://www.mangapanda.com/fairy-tail/447/2
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Natsu needs his FDK Demolition fist , his strongest move ( excluding his temporary forms ) to oneshot enemies who have durability similar to Ajeel like Jacob.
Now , if we're to buy Laxus' hype of oneshotting Ajeel , then his
casual attack should scale to Natsu's FDK Demolition fist.
Which means it's safe to assume Laxus' Red Lightning >>>> Natsu's FDK Demolition Fist as far as hype is concerned. ( May be like 10 times stronger ? )
And as recently shown , Erza was able to tank it.
Now you're telling me Erza , who was left in that condition by Ajeel , was able to tank Red Lightning ? It should've
outright killed her as far as hype is concerned. It didn't which can only mean we overestimated Laxus' strength. If Erza indeed was capable of tanking an attack many times powerful than the FDK Demolition Fist and traded blows with a person whose CASUAL ATTACKS scale to FDK Demoliton Fist , she should have been able to
completely no sell Ajeel's attacks. She couldn't , which means the attacks she tanked from Laxus are weaker than earlier thought.
The one with more feats and on screen fights in this case is Erza. Laxus has got only 2 feats in the Alvarez arc , one is oneshotting Historia of Hades ( who was fodder at that point ) and killing Wahl with his strongest attack , and giving it his all in that attack. Point to be noted since Laxus' Red Lightning went beyond Lightning , Wahl's lightning resistance suit was cancelled and his inherent weakness of lightning of the Machias race again came into play. So killing Wahl = Using Laxus' strongest attack + Lightning weakness of Wahl. Also , Laxus was cured of his sickness at that point . So since Laxus is the guy with few feats , I'm not going to give him the benefit of doubt.
Hence , imo , August was just being paranoid. I'm believing Ajeel here now after the latest chapter.