In Tartaros Arc Natsu was the first Dragon Slayer who activated DF without outside influence.Wendy can do it now.So it's logical Natsu can do it too now.Except that DF IS also overrated when he couldn't beat mard geer with it also it debateable if he could have beat Jellal at the time. It also barely beat zero with it his other modes has proven to be stronger than DF. Natsu can't used DF ON his own will. He need something to trigger it (flame of emotions or an outside source) laxus r had to go all out because of his illness and was fighting some1 tha is resistant to his magic. End was able to stop dimaria time stop. END>=fdkm natsu. And? Erza was fighting be4 was able to stop both of their attacks that shouldn't be an excuse it's just mean the lack in the endurance department gray and natsu might have DC And raw power BUT erza has Better endurance and durability. Show me proof that gray and Natsu are over erza especially what was going on in the recent chapter erza feats r right now
just like one ajeel lost to elfman and lisanna and how Mira beat Jacob
Second Mard Geer had Curse power of 6000 at that time while Base Natsu had probably around 1000.So even DF can't cover this immense gap.But still Mard Geer couldn't react as long as DF was activated andd he got weakened.
Don't forget Laxus was sick and and Wahl had immunity to lightning,but Wahl too was weak to lightning without immunity as Machias race are weak to lightning as revealed in the fight against Ichiya & Freed VS Proxy Wahl.
Erza had recent feats because she had been enchanted by Wendy and due to DS advantages.While both Gray and Natsu has been defeating Spriggans without going all out.