I hope I am not totally uninformed here...
Obviously, you are correct in that had workers invested the same money they would reap much better returns. That, however, is not point of comparison. Some today are drawing far beyond what the wisest investment would ever return while others do not live that long. No, there is no free lunch because one must contribute into Social Security. It is not a math question but a social question.
Those were some of the first people who were covered. Most of them are dead or near death. The poor today are being robbed because of their shorter life spans while the wealthy are wasting there investment on a bad deal. This is not a program that helps the poor more than it hurts them.