Not true. There's ample evidence in history of sound monetary systems (gold/silver-backed) where savers would would invest (purchase debt or equity) in capital projects which would deliver their original principle + yield + on-top profits for the banks & entrepreneurs. The British Pound in late 19th and early 20th century is a prime example: people would purchase the British Gilt which would yield a 6% return. Of course, eventually, the BOE f'd it up and printed "paper" against the pound (literally a pound of silver metal) to pay the yield to the depositors, which ended in catastrophe!
My question remains: is it possible on a BTC standard (21M) to offer a yield against risk? What could that look like? Of course, it will likely never be "6% yield, fully backed!" - but what could it be? What could it look like? Or, are we relegated to the fact that BTC can ONLY be a medium of exchange: no yield, no investments, no capital, just MOE...?