Bond king Bill Gross took a beating last month when he proclaimed the death of the cult of equities. We took a shot at him for that — as did pretty much every other nattering nabob in the investing world.

We should have kept our mouths shut.

Maybe Gross got too much sun on his summer vacation, because in this month’s missive, the guy is phoning it in.

When Gross said a month ago that stocks are priced to deliver a long period of disappointing returns, well, he may very well be proven correct — eventually. Lots of well-regarded fund managers make that case too, from John Hussman of Hussman Funds to legendary investor Jeremy Grantham of GMO.

Rather, it was Gross’s argument that was faulty. Stocks may no longer deliver the same sort of 7% average annualized returns they have for, oh, a hundred-plus years — but not for the reasons Gross laid out.

But now, in his September letter, Gross once again takes us through his case for a long period of underperformance for both stocks and bonds — and then gives some actionable investing advice.

This — this — is what he says you should do:

“If I were an individual investor, I would do this: Balance your asset mix according to your age. Own more stocks if you are young, but more bonds if you are in your 60s, like myself. If you choose an investment advisor, a mutual fund, or an ETF, make sure that your fees are minimized.”

Stop the presses.

The manager of the world’s largest mutual fund — PIMCO Total Return A (MUTF:PTTAX) — is telling us the same thing every investment adviser, financial planner and personal finance book, magazine, website, newsletter and gum wrapper has been telling us to do for, oh … the last 30 years.

Make no mistake: It’s excellent advice. Asset allocation, diversification and minimizing costs are what every long-term investor must do.

InvestorPlace’s own Editor Jeff Reeves made the basics of portfolio allocation plain, clear, succinct and amusing in this video.

And indeed, what Gross recommends is so basic, it’s best explained while wearing a Hawaiian shirt: “Take 100, subtract your age, get the percentage of equities you should hold.”

Once again, it’s not that Bill Gross is wrong. And, at least this time around, his reasoning is solid. But somehow we expect more insight from a guy who manages a fund with more than $270 billion in assets.

What’s Gross going to tell us next month? Buy low, sell high?