Would you rather be told you're not going to get a stable job as a researcher when you're 21 and first applying to grad school or at 28-35 when you're finally told you didn't get any interviews for a tenure track job?
There is such a lack of permanent research positions compared to postdocs and PhD students that I'm not even sure it's selecting for the best people.
on top of this you also filter out anyone who doesn't perfectly stay on this high-stakes pipeline from age 14 to tenure, which is probably not good overall for science.
economics is actually pretty close to working this way already. indeed, the job market for economics PhDs is much less dystopian than say life sciences. but there are tradeoffs.