It's unrealistic to assume the other sons of Midgarsormr are as strong as Bahamut, at least not the Bahamut that we know. His power was easily enhanced by the aether-infused prayers of his followers, so primal strength will vary from summoning to summoning. Louisoix had to become a god himself JUST to halt the destruction, but even then he couldn't completely destroy him. We don't know how strong Bahamut was in life though.

Middy is also leagues beyond our level. Even though his body is obliterated, his spirit alone could have killed us if Hydaelyn didn't intervene. Yes we fought him, but that was more for his own enjoyment. He is still very much alive of course :P