As someone who followed Intelligent Investor (and Klarman's Margin of Safety concepts) as an amateur who made good annualized returns, my partner and I stayed away from the modern tech stocks. We basically agreed with what you say about the risk on the performance of a company like FB: if things go bad, there's no real moat or tech or assets that comes close to the market cap of the company.

What's still reasonably valid is the concept of both moats and float, both of which I think you can get indications of in the 10-Q/A reports that aren't always reflected in current expectations.

Also, focus on where you can win. You aren't pricing AAPL better than the legions of professionals over 5 years, but the boring small-mid cap stocks that are too small for major funds to care about have more opportunity.

And finally: this is why indexing is such a huge thing. This stuff is hard, and using a low fee fund to track the market lets you live your life instead of having an extra job. I personally quit because while the % was good, the scalar wasn't worth the time invested.