Earlier quoted context omitted.
They aren't beating inflation right now, but historically they have. ~5 years ago interest rates on savings accounts were roughly 5% and inflation was 3-4%. Empirically, people actually saved less during that time (although there were many other confounding factors).
Point taken, but we're still arguing apples and oranges. Savings accounts historically maybe earned a percent or two above inflation. There's very little incentive to just let money sit in a savings account at those rates. Even extremely low risk investments are better.
Where does an investment get its value from? If saving gives me 3% but investing 5%, how does the deflationary nature of the currency change these two numbers? Surely investing gives a greater return as value is created regardless of whether the economy is inflationary or deflationary. You know, we have only had pure fiat money for the past 40 years. Before the we advanced from the dark ages to the 21st century with a deflationary system.