Also I somewhat question that money will have same purchasing power in future if either of population and productivity growth fails. The idea is that you save n

Also I somewhat question that money will have same purchasing power in future if either of population and productivity growth fails. The idea is that you save now and in future there is enough labour to buy... Which is likely to fail. You can make numbers look like anything. But that does not solve the issue that people need to be willing to do something for you for price you can pay.