A few commenters are noting that Gross is just talking his book with this pessimistic outlook.

To be fair, he's had a consistently pessimistic long view over the years.

2010:

Several months ago I rhetorically asked whether it was possible to get out of debt crisis by increasing debt. Yes – was the answer, but it was a qualified yes. Given that initial conditions were favorable – relative low debt as a % of GDP, with the ability to produce low/negative short-term policy rates and constructively direct fiscal deficit spending towards growth positive investments – a country could escape a debt deflation by creating more debt. But those countries are few – the U.S. among perhaps a handful that have that privilege, and investors, including PIMCO, have strong doubts about U.S. fiscal deficits leading to strong future growth rates.

https://www.pimco.com/insights/economic-and-market-commentar...

2011:

Bond yields and stock prices are resting on an artificial foundation of QE II credit that may or may not lead to a successful private market handoff and stability in currency and financial markets. 15% gratuities may lie ahead, but more than likely there is a negative two-bit or even eight-bit tip lying on the investment table. Like I did 45 years ago, PIMCO’s not sticking around to see the waitress’s reaction.

https://www.pimco.com/insights/economic-and-market-commentar...

2012:

We are in a “New Normal” world where the negative effects of private sector deleveraging are only being weakly addressed by monetary and fiscal authorities. If so, then Treasury yields should stay low and my money market fund should continue to read “.01%.” The “cult” of equity – or better yet the cult of “total return” – for both bonds and stocks – is over, if that definition presumes a resumption of historical patterns anywhere close to double digits. The era of financial repression continues.

https://www.pimco.com/insights/economic-and-market-commentar...

2013:

What if zero-bound interest rates define the end of a total return epoch that began in the 1970s, accelerated in 1981 and has come to a mathematical dead-end for bonds in 2012/2013 and commonsensically for other conjoined asset classes as well? What if a future epoch favors lower than index carry or continual bouts of 2008 Lehmanesque volatility, or encompasses a period of global geopolitical confrontation with a quest for scarce and scarcer resources such as oil, water, or simply food as suggested by Jeremy Grantham? What if the effects of global “climate change or perhaps aging demographics,” substantially alter the rather fertile petri dish of capitalistic expansion and endorsement? What if quantitative easing policies eventually collapse instead of elevate asset prices? What if there is a future that demands that an investor – a seemingly great investor – change course, or at least learn new tricks? Ah, now, that would be a test of greatness: the ability to adapt to a new epoch.

https://www.pimco.com/insights/economic-and-market-commentar...

2015:

This is all ending. The successful portfolio manager for the next 35 years will be one that refocuses on the possibility of periodic negative annual returns and miniscule Sharpe ratios and who employs defensive choices that can be mildly levered to exceed cash returns, if only by 300 to 400 basis points....

I wish to still be active in say 2020 to see how this ends. As it is, in 2015, I merely have a sense of an ending, a secular bull market ending with a whimper, not a bang. But if so, like death, only the timing is in doubt. Because of this sense, however, I have unrest, increasingly a great unrest.

https://www.janus.com/bill-gross-investment-outlook/may