While at bond giant Pimco, Gross had been a proponent of the "new normal" idea that economic growth and market gains both would be muted in the years ahead. The idea, when espoused around the time of the financial crisis, didn't particularly pan out. Stocks rode trillions in Federal Reserve money printing to historic highs and the bond market, despite multiple predictions of its demise, has held in there as investors have continued to seek safe haven plays.
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Gross acknowledged his own whiffs in predicting and, moreover, scoffed at his peers for still clinging to the "new normal" notion, which he said depends "on the less than commonsensical notion that a global debt crisis can be cured with more and more debt."
He also talked his own book, recommending investors buy into the idea of an unconstrained fund the likes of which he has been running at Janus since heading there last fall after a much-publicized breakup with Pimco.
At the same time, the fund pitch served as a rejoinder against criticism leveled recently by some of his competitors—in particular Jeff Gundlach at DoubleLine—that unconstrained funds are too opaque.
Read MoreGundlach vs. Gross? The 'unconstrained' debate
"Active asset managers as well, conveniently forget that their (my) industry has failed to reduce fees as a percentage of assets which have multiplied by at least a factor of 20 since 1981," Gross added in the letter. "They believe therefore, that they and their industry deserve to be 20 times richer because of their skill or better yet, their introduction of confusing and sometimes destructive quantitative technologies and derivatives that led to Lehman and the Great Recession."
Investors, he said, should start expecting occasional negative annual returns and positive returns that often will run no more than 4 percent or so.
"As it is, in 2015, I merely have a sense of an ending, a secular bull market ending with a whimper, not a bang," he said. "But if so, like death, only the timing is in doubt. Because of this sense, however, I have unrest, increasingly a great unrest. You should as well."