It isn't so much that P/E is rubbish but that its utility as a proxy metric assumes approximately flat revenue growth. This assumption is no longer true for a significant percentage of the largest companies, many of which are demonstrating large non-zero revenue growth rates, both positive and negative. If you are looking at companies with high revenue growth, there are other metrics used to determine if they are "cheap" or "expensive". Amazon is a great example of a company that is "expensive" by value metrics like P/E but actually pretty cheap by metrics with more applicability to revenue growth companies.

The problem is that many investors apply metrics, like P/E or book value, blindly without understanding the assumptions that must be true for the metric to be a meaningful measure of value. It is even more complicated inasmuch as some companies fall into an ambiguous gray area when it comes to appropriate valuation metrics (I'd argue Apple is one such company).

Like with any analysis, there is some work to make sure the statistical model actually captures what you intend to measure.

> The problem is that many investors apply metrics, like P/E or book value, blindly without understanding the assumptions that must be true for the metric to be a meaningful measure of value. It is even more complicated inasmuch as some companies fall into an ambiguous gray area when it comes to appropriate valuation metrics (I'd argue Apple is one such company).

This is obviously the core of the issue. But you'd be surprised at how often it is that these concepts surrounding P/E are parrotted constantly at many leading financial firms and schools.

But I think the opposite case still kind of holds, that with P/E you can at least see if a company is most likely not overvalued. And that was the issue in question ("everything is just gambling").

P/E doesn't even tell you that. Companies with negative revenue growth rates often have low P/E ratios but these are often overvalued and poor investments even then. Sophisticated investors, and therefore market pricing, take all of this into account when valuing companies. All trivial nominal measures of stock value were completely arbitraged out of the market many years ago.

There are still measures that correlate well with low risk and strong returns for some subset of companies, but identifying a subset and building valuation models for them is non-trivial (e.g. I typically use risk models for revenue growth in comparative valuation which don't even apply to most of the market). If it was as simple as looking at a trivial ratio of public numbers, everyone would already be doing it.

I've been investing a long time and the markets have changed a lot over the decades. At this point, I think most of the investing advice from several decades ago is obsolete because it is based on assumptions that aren't actually true today. Investment advice and heuristics have a shelf-life. Most people aren't going to build a portfolio strategy from first principles, it is a lot of work, hence the popularity of index funds.

I certainly didn't want to suggest that P/E is a reliable or sufficient indicator for good investments. It was just about this claim that everything is just gambling at this point.

Granted it was then perhaps a bad example, as it doesn't take into account the value of the companies possessions.

I just wanted to give an example to say that you can check things about a company beyond the stock price, which may be inflated by gambling. If a stock is "gambled" to the moon, it assume would have a very high P/E. I'm not actually an expert on those indicators, haven't looked into them much.