Between his mantra and the sheer power of his devil fruit, it's safe to say Enel would still be one of the most powerful men in the world. Would Enel rule? No. Would there be others besides Luffy who could beat him? Sure….but not many, and not without the right abilities or equipment. Given the proper environment, Enel alone could produce the equivalent of a buster call, could detect and destroy entire fleets of ships before they even got near him.
Not every character in One Piece should be judged by the strength of their character, resolve, or dreams.
There is something to be said for raw power, otherwise devil fruits wouldn't even matter in OP, but we know that they do - and lightening is pretty damn powerful (it's super-fast, hotter than fire, turns sand to glass, melts ice, etc.). Whether or not some other characters have "stronger hearts" is irrelevant, because even in Oda's world, that's not the last word. Like any good story teller, there are some rules to Oda's world, and they are not that extremely detatched from common sense that such a powerful raw element would become weak so easily. It's very likely that Oda sent Enel off to space precisely because he was overpowered and his active presence would change the balance in place back under the clouds.
….and btw, regarding those debates over lunar survival, it's safe to assume Oda has given the Moon some manner of atmosphere, considering that non-logia creatures apparently live there as well.