I agree completely. By a mathematical standpoint let's do some measuring.
Okay, so usingso using this video as reference to in-game size you could estimate that, by referencing the distance to the ground to Deathwing is to be around 50 meters off of the ground; this can be confirmed by this article's mentioning of the tower they're in and about the view, which look about right... [Reference Image]
Now, if you compare the distance vertically to the length of his entire body, they appear to be the same give or take ten meters. Being generous and giving him 20 meters, we have one dimension down. Now for the sake of making this short and less painful, let's also consider his wingspan to be about 100 meters, and then just multiply it and ignore the empty space. Again, this is to be nice in favor of the "scary" Deathwing. Now, let's give him a thickness of say... why not, ten meters.
Okay, so we have dimensions, let's calculate volume:
70*100*10 = 70,000 m³
Let's then assign both Dragons an equal density in comparison to mass, let's use the element Pb (Lead) which has a density of 11,300 kg / m³
(11,300 kg / m³)* 70,000 m³ = 791,000,000 kg = Deathwing weighs no more than 791,000 Metric Tons.
Bahamut emerged out of a "lesser moon" - if we assume the lesser moon is roughly the size of the moon Miranda, then you can estimate the a 1m thick skin flying off in force. size-comparison picture. We can also guess his size based on this and the fact that he looks a few kilometers in length and possibly have a wingspan of several kilometers as well.
If we severly simplify Bahamut's size to say (2 km * 1 km * 1 km) which in lead would make him weigh:
(2 km³ * 1.0×10e+10) = (2,000,000,000 m³ * 11300) = 2.26e+13 =
2.26×10e+10 Metric Tons
Bahamut weighs roughly (22,600,000,000 / 791,000) = 28,571 times heavier than Deathwing and a LOT bigger - there is ZERO contest here seeing as he couds piss out a deathwing.
(3,964,776.51 km² / .001) * 1m = 3,964,776,510 m³
(3,964,776,510 m³ * 11,300kg = 4.4801975e+13 kg
Now let's consider that if Hydaelyn is nything like Earth, then the Atmosphere extends to the Kármán line which is roughly 62 miles, or close to 100,000 meters high. If Dalamud is half that distance at 50,000 meters then we have a distance to measure speed. Examining the video, you could guess that it takes roughly 3~5 seconds tops for most of the pieces in the area of Eorzea to be hit. Let's say it takes 5 seconds. Let's then take say...
a piece that is .0001% hitting Deathwing... Let's do it in Newtons then compare that to a Nuclear blast.
(50,000 m / 5 s) / (4.4801975e+13 kg * .000001) = (44801975 kg * 50,000 m / s) = 224,009,875,000 N
The the original fission bombs used in WWII only produced around 300,000 N which means .0001% of a piece of Dalamud hitting -should- technically hit with a force of 746,699 Fission Bombs. Of course this is wrong because there's still an Eorzea, so he's been dumbed down quite a bit. I also want to point out that Dalamud appears to be even smaller than Dione, and yet even if you reduce these numbers by half, the numbers are still shocking.
I might even have made some mistake, but I'm tired as shit and this is some quick calculations. Even if you significantly dumb down the numbers, you still have a power vacuum Deathwing is too feeble to even try to fill.
ALSO! The key that falls from Dalamud; if it is 500m high, 30 m wide, and 10 m thick (going low) it's volume is 150,000 m³, it's density in Titanium is 675,000,000 kg, and calculate gravity (9.78033 m/s2) you get 33,075,000 N I believe. Hm... some things not lining up with the video... This video defies Physics! Oh wait... this is Final Fantasy... Even if I fucked up, the numbers will still be hella large.
tl:tr
Bahamut is 28,000 times heavier than Deathwing in lead - and 100,000th of Dalamud hitting Deathwing could carry enough force to effectively nuke him out of existence - Discussion over.