Savings are invested into creation of long-lasting capital goods that are just as real as grain reserves or oil stockpiles, and that yield a positive return ove

Savings are invested into creation of long-lasting capital goods that are just as real as grain reserves or oil stockpiles, and that yield a positive return over the original investment - companies being "massively more productive per worker" isn't the exception, it's (hopefully) the rule. Yes there is risk involved and some investments won't work out, but that's why you diversify and make conservative assumptions. (Now if the economy was projected to stagnate in the future, you might have a bit of a point. But since our economy is growing, even "paper" wealth like government bonds can easily yield a positive return.)