well Jins if they do exist they do have advantages over humans, i dont know much about christianity but humans are not the best creatures of God, what about Angels? arent they strong,powerfull and smart?
about the Devil
well iam not sure but this creature supposed to be ancient and wont die till day of judgment.
some say he was an angle and became the Devil when he diobyed God, other say he was a Jinn.
but then both Jins and Angles are belived to be created from the same thing. like humans and animals were made from mud.
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Ifrits are Jinns, but stronger and devilish i guess
as i said earlier they have different sizes and abilities.
all the above is from Religiouse point of view.