Lex Luthor is a human. Supposedly having no superpowers (he would win the Olympics, the Chess championships, but still). Superman is like a noble in a fairy tale: better than ordinary people in every way and obviously more deserving of the princess.
Most villains are misfits, have something wrong with them, and don't fit our values for what make people superior. The hero is superior even if today that doesn't necessarily mean being of noble birth.
In fact heroes are more likely to be born for their special, chosen role. Superman fits well.