JP Morgan says public tech companies are trading at one of the smallest premiums in their history, while the FAANGs' share price-to-earnings ratio has dropped by more than 60 per cent since early 2017.
Next week we will discover the real extent of the damage.
Amazon, Apple and Facebook will report their latest results, along with Tesla and Microsoft, which was during December the world's most valuable company.
Will their numbers be sufficient to deliver a boost for the sector, or will they unleash a new round of sell-offs?
It will certainly be judgment day for Amazon, whose founder and chief executive Jeff Bezos is lying low after his dirty laundry was aired in public.
Earth's richest man, estimated to be worth US$160 billion, announced he was divorcing his wife MacKenzie.
While the public was gripped by tales of jaunts on private jets with his new lover, the TV news presenter Lauren Sanchez, investors are keen to learn whether it was business as usual in the Seattle headquarters.
The forecast seems positive. Amazon, the world's largest online retailer and leading cloud computing provider, is expected to defy the wider downturn when it reports on January 31.
Early market data suggests it will beat estimates on Christmas sales in the US, despite a general drop in the UK.
But its previous results were disappointing, driving down shares as much as 10 per cent, and it warned at the time that operating profits could be as low as US$2.1b - flat with 2018. Despite this, Amazon's outlook is positively rosy compared with that for Apple.
The iPhone maker, which reports on January 29, has already warned of a slump in sales.
George Salmon, an analyst at Hargreaves Lansdown, predicts it "could sell fewer than 200m iPhones for the first time in four years".
Tim Cook, the chief executive, blamed Apple's new policy of offering battery replacements for older models, as well as a general economic slowdown in China. But few believe this to be the whole story.
The smartphone market is widely expected to stagnate this year, and Apple is ill equipped to face that.
Apple and Amazon are increasingly turning to services which can bring in revenue continually, with healthcare a target.
Michael Hewson, an analyst at CMC Markets, says Amazon has the edge. The shopping giant is competing with Apple for smart speakers and tablets, where it shows strong sales. Its most recent report also showed growth in its advertising business, which represents a small but real threat to Google and Facebook.
As for Facebook, which reports on January 30, storm clouds are gathering. After years of high margins and high growth, Mark Zuckerberg warned in October that investors should expect slower progress in future.
Facebook's user base is pretty much at "saturation" in Europe and North America, and its sister services - Whatsapp, Instagram, and Facebook Messenger - have yet to prove their moneymaking prowess.
Zuckerberg has signalled that he thinks internet users are recoiling from semipublic posts towards private and disappearing messaging, but it remains to be seen whether Facebook can profit from that shift.
Sales of its new Portal video-calling device are unlikely to make much difference, even if it were a success.
And the company is exposed to China's slowdown to a degree most investors do not appreciate: though it remains banned by the Communist Party, several billion dollars of advertising is tied up in Chinese companies and their intermediaries.
Facebook's biggest problems, however, are political. After years of "moving fast and breaking things", and following several backfired attempts to smother its critics, Pivotal Research analyst Brian Wieser believes that the company is now "toxic" and further regulatory action, whether in the US, the EU or elsewhere, is inevitable.
That will, of course, mean fines, perhaps similar to the record €50 million ($83.6m) penalty dished out to Google by the French data regulator this week.
Wieser cites that ruling as evidence that Eurocrats are not impressed by Silicon Valley's attempts to comply with new data rules and that more such penalties are likely very soon.
But the more serious problem for Facebook is that the threat of regulation will force it to operate like a slow-moving "corporate citizen" rather than a nimble start-up, spending ever-increasing money on removing dangerous content and consulting carefully about every new project it launches. It could even be broken up by competition regulators.
On the topic of fines, Google, whose parent company Alphabet reports on February 5, is also politically vulnerable but safer than Facebook.
New European data protection regulations have actually helped it somewhat, wiping out smaller rivals that lacked the capital to invest in compliance.
Its search engine, the largest part of its business, is still the most effective and successful example of digital advertising.
For that reason, according to Colin Sebastian, a senior analyst at Baird, it would be foolish to sell.
Its big weakness is in cloud computing. There is a running joke in the industry that Google, one of the largest and first investors in massive data centres, has yet to catch up with Amazon's data-storage service.
Many fear Google has missed the boat on this "massive opportunity". Do not expect to hear much about it either: Google still hides cloud computing in the "other bets" section of its report, making it impossible to untangle from its blue-sky investments in internet balloons and driverless cars.
All these companies, despite their differences, may face one larger problem. At the start of this year Vincent Deluard, a strategist at INTL FCStone, wrote a provocative note proposing that the era of high-flying tech stocks is over for good.
"If technology is everywhere, the tech sector no longer exists," he said.
"If the tech sector no longer exists, its premium is no longer justified."
His argument is twofold. First, most of the FAANGs' competitors are now copying their methods well enough that they are no longer unique.
If legacy car manufacturers such as BMW are making electric cars just like Tesla, why should Elon Musk's company be trading at so many more multiples of its earnings?
Second, today's tech giants may simply have exhausted their capacity for innovation.
"They are competing in existing industries versus creating new industries," says Deluard.
"When the iPhone came out it was something that created the market from scratch, and it took the industry several years to catch up."
Now, the industries they are trying to move into - such as medicine, grocery shopping and banking - will struggle to give them such explosive progress. Hence share premiums "reflect an era of growth that is unlikely to reoccur".
"In 2017 people thought Mark Zuckerberg was running for president, and Sheryl Sandberg was touted as this source of inspiration for young women," Deluard says.
"Just saying it today seems laughable... there was this almost mystical aura around them that could only compare to what Steve Jobs was able to command after his third resurrection. It turns out they were humans after all."
