Ego = sense of self. It is usually used as a derogatory term but that is a mistake as there are positive and negative aspects of ego. Kevin has a very strong sense of self, is comfortable and confident in his own skin. nobody Would call him egotistical because his ego is very strong but well balanced.
Yaya on the other hand allowed the negative aspects of his ego to dominate at times which made him seem precious and self centred. I’m not sure there is any correlation between genius and ego, we all display both negative and positive aspects.