Not a downvoter (nor a financial expert) but to check the argument seems at least reasonable to check whether the proportional return of Vanguard funds has decreased as the fractional amount of money invested with them vs. the total stock market has increased. Seems unlikely the answer is yes (probably because in fact you are not investing in "nothing" -- there's value in having money itself, same as interest at a bank, and you are investing in giving that money to lots of companies, not just one, and that's what you're making profit off of. So long as money generates money, why should the return taper off?)

Probably an interesting number itself knowing what the fractional amount of money flowing through Vanguard is as a proportion of the total.