Mutual funds make up a trivial portion of worldwide index-fund investing. I used to work at Wells Fargo, starting several years after McQuown and the first generation of indexers had already moved on to other things. But at the end of the day, we were delighted to have him out there winning hearts and minds for us. Index funds naturally lower the costs of investing because they eliminate expensive investment managers and traders, and they cut transaction costs by reducing the volume of portfolio turnover. The index has no costs whatsoever, but investors have management fees, commissions, research expenses, taxes and so on.
Costs are a leak in the bucket of performance.
The most zealous advocates of indexing have claimed just that since 1971. But it isn't true. It is possible to beat the market. But it's not possible for everyone to beat the market all at the same time. So that means that it's very, very hard to beat the market.