That right there is a contradiction, you say he was engulfed yet you suggest that the fireball had any force behind it which would the. Push him outward, so it is one or the other. His flames were always the same, he just released more flames, there was no statement in change in temperature, just the amount of energy released, which is less significant than when he fought in Alvarez. Madmole was specialized in armor based magic yet got fried, Jacob was not burned at all despite being smothered by more energy than what Madmole experienced. That does not change what level power they took, if Natsu had gone FDKM, Madmole would be in worse shape than Jacob did, likely dead, as a standard FDK technique killed powerful beings such as gods. As far as I am concern, Anime only serves to clarify certain scenes, anime tends to exaggerate what was shown in the manga and should not be taken as one hundreds percent canon, the only thing canon is that he worked with adding Acno back story. So none of the Anime filler for Mira vs Jacob fight are canon. There was no proof that he as on the verge of defeat, he was already in a position that he could not fight back. It does not matter, as physical attacks are still powered by magic to a degree, it has been stated that the Spriggans scale to each other, and one of them (not the top three) can destroy countries, and Wall’s Etherion is based on radiation energy with nuclear fusion so the energy emitted are large country level at best. So that gives the statement valid claim. Etherion from the magic council is scaled to multi continent from the sheer size of the blast, it is called Scaling, yet Irene compresses an entire country the size of the US. Acno did not show any feats to match that or Merc, so by your logic Acno is weaker than most people in FT verse