I suspect a number of those are the types of companies that if they had to turn a profit, could do so by cutting back investment and taking profits, in addition to reasonable amounts of corporate restructuring and investment. Many of them are at least plausibly in that category. Some of them are not (TSLA for instance is not in a position where they can coast right now).

1999 was full of companies where even if they had captured 100% of the relevant market at the time, would still not be turning a profit or be viable businesses. They were fundamentally built on the presumption that 2015-levels of internet penetration and hardware capabilities in the first world would be obtained in 2001 or so. It wasn't just a matter of "they were investing what could have been profits into further growth", it was a lot more like "they were taking VC money and setting it on fire and calling that a business model". It is not the same today. (Modulo my caveat about advertiser money above.) It may be bad. But 1999 was insane.

I can easily see a correction, even one we'd consider large. But I would bet the "correction" doesn't undo more than two years of stock market growth when it happens, and it may not even manage to cause a recession, or if it does, a very minimal one.