the returns will be as guaranteed as any other form of investment and as with any other investment will depend on the level of risk taken
As for where have the funds come from
most from selling or transferring assets held in their own name that was going to be funding their retirement but taxed at marginal rates, but now being held in super funds (mainly self managed) and being tax free
Expecting the government to fund your retirement in the future is living in fantasy land unless you can mange to live on an absolute minimum.
As the population ages the need for people to fund their own retirement will increase, which is why they would have been better off dropping the tax on contributions rather than payouts
