This argument doesn't hold up against Superman killing Zod though. Zod was just as powerful as him, and would likely have surpassed him if not killed. Plus, MoS was an origin story, it was his first fight. Of all the things in MoS to complain about, and I'll admit there were many even though I loved the movie, killing Zod doesn't seem to me to be one of them.
Superman is strong enough to snap Zod's neck but not strong enough to just hold his head in place and let the humans escape, and then knock out/restrain Zod after that?