For what it's worth, Khan wasn't speaking about all 23rd century people not being able to break bone. He was making a sarcastic or insulting remark aimed at Spock, saying that if Spock can't even break rules, how can he be expected to break bone. Khan in "Space Seed" was also very arrogant about being better than other people. In “Space Seed” he tells Kirk, “Captain, although your abilities intrigue me, you are quite honestly inferior. Mentally, physically. In fact, I'm surprised at how little improvement there has been in human evolution." He talked about how he'd have eventually become the sole ruler on Earth in the 1990s and would've offered a world like Rome under Caesar. When Marla told him he may not like living in their times, he said he'd have to mold them to his liking. I don't think he meant that would be done peacefully. Characters like Khan were a recurring theme in all versions of Trek: incredibly gifted people who were also incredibly flawed in some tragic or criminal way.