There's a bit of a counterpoint to this: with papers, it's easier to point to your body of work (peer-reviewed and, if you're good/lucky, peer-understood-and-approved) as clear evidence that you can do research. Without papers, or with very few papers, that evidence has to come from somewhere else. My understanding is that somewhere else is usually recommendations, from your advisor and other people in the field. Some reasons to dislike that system include:

1) it gives advisors a lot of influence over the student's career (obviously, if you have an actively hostile advisor things will be hard in any system, but I have known successful faculty who had indifferent fund-and-forget-style advisors who wouldn't know enough about the student's field to write a good recommendation)

2) informal "I like this person, hire them" networks tend to select for people who are like current participants in the network

I agree that a coarse "do they have at least x papers?" way of evaluating researchers is silly. But it's not crazy to have 10 papers when you graduate. That's about one paper every 6 months in a 5-year program. Six months is a long time, almost a thousand hours of work. If three people are focused on a project, it's pretty plausible to get a cool result in six months.

I appreciate your perspective. The people on the hiring and tenure committees as far as I can tell usually don't/can't evaluate quality directly so they instead focus on proxies like the total number of papers and what journals someone published in. I'm fairly against total publications as a proxy but I hadn't considered how it fared against these alternatives.

Personally, if I saw someone published a ton of papers during their PhD, I'd question the quality and importance of their research. Quality tends to decrease with quantity in my experience. And it appears too easy to fake importance. In my field I watch out for vague words like "novel" and "fundamental" in paper titles as evidence that the work is probably overhyped. I'm fairly well read in my field and I can sense the disappointment in people when I tell them that their "great" idea was done before, particularly when it was done better and/or a long time ago. (I take no pleasure in doing this. I just wish people spent less time reinventing the wheel.)

I think I could have had 10 papers during my PhD if I focused on easily-published things and "salami-sliced" my papers. But I focused on what I thought was more important and made the scope of each paper larger than normal because it saves readers time.

Proxies that are characteristics of the researcher might be better (or at least should be considered), like the willingness of the researcher to put "skin in the game" so-to-speak. I'd have a lot more confidence in research conducted part-time by someone on their own money than someone using another person's money (which has much less risk). Taleb has written about this as I recall.

I'm on many hiring committees and I try to evaluate quality of research as well. While you cannot spend too much time reading all these papers in full, just looking into them for a few minutes usually gives a sense of where the results fit and how significant they are. A good recommendation letter is useful here: especially for PhD research, the advisor can briefly explain what motivated the problem, how the result was found, what is its significance (from their own point of view of course), and what the candidate contributed to it. The reco letter can also explain why the candidate has fewer/more papers than usual, etc. At the end of the day, there are many objective-looking criteria, but in my experience people still make gut decisions based on their overall impression and then look for criteria to rationalize it. I find this to mostly work OK though, and better than having purely objective criteria and sticking to them no matter what.

For additional context, Stonebraker helped make Postgres and was the Turing laurate back in 2014.

https://en.wikipedia.org/wiki/Michael_Stonebraker