I'd hate to work at a place where the backlog comes from the PM and the requirements come from a mix of PM and UX. Do you really think your PMs know that much more than your Engineers, Data Scientists, Ops/Business, etc.? This just sounds like something the type of PMs most of us hate, the type who insist on being the main character, would say.
Yes, PM's are absolutely supposed to know that much more about what the customers need. That's their job. They're constantly talking to customers; engineers are generally doing that only occasionally, if ever. They're not trying to be the "main character", but their entire job is to be the point person for integrating all the stakeholders' needs and making prioritization decisions. It's organizational needs, not ego-driven.
Sometimes products are simple and straightforward enough where you don't really need a dedicated PM, but then the lead engineer often just winds up informally taking on the same responsibility, and at some point there's enough success and complexity that it needs to become a full-time dedicated position.
I'm really curious how you've arrived at the perspective that engineers and data scientists know as much about customer needs as a PM, that they learned via channels outside of the PM? I've certainly never worked anywhere where that was the case.
