Yeah it was hard to see Superman getting kicked around like that, but you do have to remember it wasn't that he was just powerless. He was surrounded by krytonite and his body was sickened and weakened by it. He wasn't just a normal guy at that point, he was hurting bad.
Now logically if you stop right there it makes sense to me, but then we next see him getting a super recharge from the Sun and going back and lifting the same very large chunk of kryptonite landmass into space. All I can attribute this to is his incredible will. Which is very much like the comic books. We even see the intense painful look in his eyes as he is rising higher into the sky holding "New Krypton" up. That is something to me they got right, Superman sacrificing himself to protect as Lex said BILLIONS of people no matter the personal cost.
But yes it would have been nice to see him at least get a couple of good hits in..especially one square in Kal Penn's face

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