The calcs make too much assumptions to be considered scientific. The only thing scientific are the equations. Even the way they assume there is a difference whether the damage was "completely destroyed" or "just pulverized" is not scientific at all. Think about it: Natsu displayed fire that could melt rocks in the GMG before. Why would you come to the conclusion that the rocks were merely pulverized instead of melted? That and sometimes I see obvious scaling errors. It's not hard to see when an attack is city level or town level. It destroys an area on the level of a city/town. Some attacks are so obviously not capable of leveling a town it's not even funny.
Also, to clarify a few things: CSK was nowhere near the size of a mountain. I won't go over this in detail, but the area where they are fighting in has mountains. CSK obviously wasn't as large as those. Cube was not the size of Magnolia Town. You can actually see the difference in size between the two as the cube hovers over Magnolia. I can grant cube small town status (like the one Gildarts fell on), but realize that Magnolia in it's whole is huge. Magnolia is easily larger than a mountain. It's actually surrounded by a mountain range. Capital cities like Crocus (the only true city in the sense of a modern city-scale), can possibly contain multiple Magnoliga's.
AoE also isn't everything. Ikusa-Tsunagi's slash is the largest attack in this series, covering the span of multiple towns in length. Natsu was able to shatter Ikusa-Tsunagi and his sword with demolition fist. In a head on collision, demolition fist would likely be stronger than Ikusa-Tsunagi's slash, despite being smaller in scale. I didn't get the same sense with thorns and meteor blade though. In a head on collision, meteor blade would hack away at thorns. Weaker people like Natsu, Sting, Rogue, and Gray have all hacked away at thorns. Obviously if Sting and Rogue can cut through thorn brambles, then it's not some sort of super durable substance. Obviously thorn brambles have never been used to destroy an area on the scale of a city. So why should we even consider it being on the level of FDK roar? Think about it: Head on collision between the two, FDK roar would likely swallow all the thorns whole and incinerate them.