The definition of 'genius' is subjective. I, personally, think that he is nowhere near a genius, by my definition of the word. However, the definition of genius is as follows: "a person who displays exceptional intellectual ability, creativity, or originality, typically to a degree that is associated with the achievement of unprecedented insight."
Typically, I think of a genius as someone like Tesla, Newton, or Da Vinci, people who make vast improvements to their respective fields. Kishi, not so much. Is Kishi exceptionally intelectual? I'm not sure. Is he creative? Sure. Is he original? Not really. He uses DragonBall and mythology as his main inspiration. Has he done anything that no one has done before? Not really. Ninjas with superpowers have been done before.
I say, no, he's not a genius, but you can say that he is.
