There's nothing in there that indicates Norman had super strength. Spider-Man is sturdy, but he's not Superman or the Hulk. A punch to the back of the head is still bad news, when the story calls for it.
During Ditko's run the Green Goblin didn't exhibit super strength. He used weapons to fight. Ditko thought these things through, if the Green Goblin was supposed to have super strength then he'd be shown using super strength.