It's easy to build a 401(k) portfolio that reflects the conventional wisdom on long-term investing. You put your money largely into stock funds. You are advised to put something into bonds and move more into bonds the closer you get to retirement. But for return, you rely on stocks.

"For the long-term investor, stocks are supposed to add 5 percent per year over bonds," writes Robert Arnott of Research Affiliates, in the Journal of Indexes. Then comes contrarian shock therapy. "They don't. Indeed, for 10 years, 20 years, even 40 years, ordinary long-term Treasury bonds have outpaced the broad stock market."

If stocks made 5% a year more than bonds, it would compound to a huge difference over decades. Mr. Arnott sets out the evidence. From 1802 to February 2009, stocks actually made 2.5 percentage points a year more than bonds on average. That's the compensation for the greater risk you take by being a shareholder rather than a debt holder.

It still compounds to a lot over time, but the yearly margin is thin and for periods of as long as 68 years, it disappears. "For the long-term investor, stock markets are supposed to give us steady gains, interrupted by periodic bear markets and occasional jolts like 1987 or 2008. The opposite — long periods of disappointment, interrupted by some wonderful gains — appears to be more accurate," Mr. Arnott says.

In the 40 years from 1969 through February 2009, an investor in 20-year Treasuries made more than an investor in US stocks. So is Mr. Arnott telling us to buy T-bonds? No, not at all. This veteran challenger of received wisdom almost always springs surprises.

He's calling for a revolution of sorts in money management. "Why are there so many equity market mutual funds, diving into the smallest niche of the world's stock markets, and so few specialty bond products, commodity products or other alternative market products?" he asks.

Retail investors are offered numerous small/mid/large cap and international/domestic equity funds. Last year almost all of these lost money, many as much as 60% or more. 401(k) programs are dominated by the same names. Our fund choices may be wider than that of Henry Ford's customers, who could have any color car they wanted as long as it was black. But underneath bogus variety is a great deal of sameness. We need diversifiers.

Will the change Mr. Arnott hints at give us real choice, provide options that won't lose money in times of turmoil? Well, the change he's wrought so far, fundamentals-based equity indexes, did not do notably better than traditional capitalization-based indexes in the crisis.

But at least he offers insight about the prospects of equity-centric investing. That in itself is progress.

Chidem Kurdas maintains the blog MutualFundSmarts.com, an informative outlet for sophisticated mutual fund investors; and the blog Manhattan Capital (www.JenniferKerfuffle.com), a hilarious, libertarian news-spoof. Chidem is also a contributor to ThinkMarkets.