>>107011238Sivana wasn't the first person called to the rock of eternity, Shazam had been searching for an apprentice for a long, long time. Hundreds of years.
There was never going to be a perfect person. But it turns out that Shazam didn't need someone who was perfect, just good.
Think about it: young Sivana with the powers of Shazam would would have satisfied his envy (godlike powers mean he no longer has to be envious of his older brother) thus removing the basis of the sins to manipulate him. As a victim of bullying, he would have hated bullies.
He wanted what all young boys want: his father's approval. He could have been a fine champion. An even better one if the wizard actually taught and raised him to any degree to prepare him for his post rather than doing the destiny equivalent of a dine-and-dash.