Treating stocks as fractions of future real productivity ignores why companies sell shares in the first place. If the value of a company was wholly in its future real productivity, then companies would never part with ownership. However, companies do sell shares because they need liquidity now, whereas the future value of the company is purely speculative. Shares are but one of many alternatives for companies to raise liquidity. These alternatives provide opportunities to investors with different risk/reward profiles. As you say, there's nothing special about stocks that makes them inherently superior to other forms of investment.