When I finish reading this book, and my brain is less covid hazy, I'll explain the point better. I agree, PE ratios matter. The question is what ratio makes sense for a type of tech business. Does PEG, and other metrics capture that or not? AMZN hasn't had an attractive PE for over a decade, yet it's been an amazing investment. And historically they've been willing to overspend on their infrastructure build at the expense of now for bigger future growth. The point was, as more Tech loads up the top of the S&P500, a PE of 15 may not correlate as well, where a PE of 18-20 might be a better fit.
AMZN may also be near as big as they'll get. But, like many value investors say, it has quite the moat around it to fend off competitors. Walmart spent a ton to take on AMZN's online store, and it pretty much has failed.