He never 'clinged' to his 'mummy' his plan was to become a god by bringing in a Meteor which would threaten the life of the planet and when the planets life is threatened the lifestream wells up at that wound, and in order to do that he needed Jenova's help. With Jenova he had the ability to exert some control over those who have Jenova cell's inside them (like for instance when Cloud hands over the Black Materia to Jenova at the Temple.) And TBH I think its better to kill people with the skill of a sword then just to blast the away with magic/summons/statues in the game he was a living legend, like Cloud said: Sephiroth's strength is unreal. He is far stronger in reality then any story you might have heard about him.
Never clinged to his mommy? What the heck are you saying? He went off to destroy the world to give it back to his mother!!!
(Wait....destroy...to give back....You see this is where the insanity is coming in and really making things weird!!!)
A rock that big won't simply wound the planet, it'll kill every living thing on the earth. And by doing that, the planet itself. So it wasn't a very good plan now was it? An asteroid is about the size of a building-the Black Materia finds
small drifting planets! If an asteroid wiped dinosuars on this earth, a small planet would, unfailingly, destroy the earth.