World of Cardboard
This is why Superman almost never hits someone as hard as he can. Why, even if he says he is, he isn't hitting Rogol Zaar so hard, he could break him.
This is why Death of Superman lasted over multiple issues, taking days to end. This is why animated Superman fought Darkseid TWO other times, before finally making this speech.
A Superman who hits you as hard as he can, is a Superman who is willing to risk KILLING you. This isn't a choice he's able to make, without extraordinary circumstances pushing him to it.
Otherwise, he would not be Superman.