He is not perfect at all. He can be hurt if hit hard enough and he can definitely be broken. I've heard. "Why does superman allow himself to be knocked around around." when he isn't. He is literally in pain and when something like doomsday hits him he will feel pain. Or when darkseid hits him with his omega beam. Trust me he is not invincible, he can only do so much alone and all you need is cryptonite and he's like a human.