You guys forget something. END, or in this Natsu, is a unique character within FTverse. END was the one who created the forms of magic known as Curses that demons use (chapter 410). END is, by all means and purposes, as strong or stronger than Zeref, Acnologia, Igneel, Mavis and all other mages seen so far. And I'll explain why his basic nature enables that.
Dimaria's magic revolves around a form of Take Over in which she borrows the powers of the god Chronos and, ultimately, can even become a vessel for him. Inherently, she is able to freeze time to the world except herself. This is the core ability left over by her take over and always present. But the ability itself is borrowed from that God. God Magic.
In FTverse, there are "tiers" of magic. Human Magic, Demon Magic, Dragon Magic, God Magic, Celestial Magic, etc. Right? Each one is stronger than the last in its essence (though individual magical aptitudes can make a weaker magic stronger against another regardless) aond one trumphs them all. And in theory, God Magic is the strongest in the ftverse, right? Well, if END was created with the ability to kill Zeref and Zeref is supposedly impossible to kill because he received a curse from the God Anksheram, then END was created with the inherant ability to overcome even God Magic. Its God Magic the ability that keeps Mavis and Zeref immortal. To kill them someone would need to overcome that same magic. Thats why Zeref's curse was able to affect Mavis. Its of the same nature and degree of power and Mavis was a weaker individual. It was nothing more than a clash between 2 mages, even if they were completely unware of it at the time. Now, Dimaria's magic is God Magic so...well, do the math. END was built with the ability to overcome and counter God Magic. And its not the first time Natsu did it. He ate god flames, remember? He ate the flames of a Fire God Slayer.