So...all tech companies are overvalued as long as you exclude the ones that are correctly valued?

But PE is obviously the wrong metric for Amazon since we know it reinvests all its earnings and has proven ability to convert investment into cash flow.

This is due to Amazon purposefully keeping gross profits at $0 for years. The CapEX investment was through the roof; investments such as AWS which were criticized heavily in their infancy. It was widely known Amazon would be able to turn a profit, they decided to ruthlessly expand their enterprise.

Amazon has low margins, I think the theory with the PE is that they can increase margins after achieving market dominance and get better earnings. Walmart is still bigger so Amazon isn't there yet. And then it could also be high because of the cloud/tech bubble.