If the damage is proportional to the dimension of the blast, and I think it is, then Natsu's amp is more than crazy.
The Fire Dragon King fist put a pillar of 1mm on the drawing and the Purgatory Ougi pillar is 10mm.
If his DF Ougi is 10x the DFK strike, he is clearly the strongest character of the entire manga by far.
When he fought Acnologia, he combined the magic of 7 Dragon Slayers far weaker than his FDK mode, except for Laxus.
In my opinion, the combine power of Sting, Rog, Cobra, Wendy and perhaps Gajeel is about 1 FDK Natsu (base Natsu was stronger than combine Sting and Rog, and Cobra is still fodder. I put Gajeel around base Natsu). Laxus, this time was, in my opinion, around FDK power level, or slightly above. Saw, we had about 3x FDK power level. If we take account that unisson raid is stronger than split magic, we had about 4 or max 5x FDK power impact in that ultimate strike which obliterated Acnologia.
So Natsu, now, after only a year, can generate by himself, about twice or more the strength used to kill Acnologia ?
That make no sense he reached this level in only a year. So now, he is stronger than combine Gildarts, Red Lightning Laxus and Erza ? Reverse the gap with Acnologia himself ?
In my opinion, as I like Natsu, it is ridiculous that he can obliterate alone a foe as strong as he needed the help of 6 wizards in unisson raid to do the same.