In addition, Facebook and Google are supported by ad revenue,...

In addition, Facebook and Google are supported by ad revenue, not users, so not sure how many businesses would be splashing the cash on marketing at the moment. Apple is driven by the consumer....most of which in the US are debt laden pay cheque slaves whom I am sure will be conserving cash over the next couple of years. Then there is Netflix, a $190B market cap, with $26B in liabilities and negative free cashflow, also Netflix is now in a crowded market and its ongoing survival is driven by new content to keep users engaged and currently production has ground to a halt.

IMO these FANG stocks are supported by cheap money from the fed and the belief that some greater fool will buy them at a higher price in the future. Nothing more.