> someone needs to say what to do, someone needs to do it, and someone needs to say if it's been done

I agree, but if you zoom out, "someone needs to say what to do" and "someone needs to say if it's been done" are the customers and end users. Will they still need product managers, software engineers, or QA in the middle? I think so because many customers will need help from experts with domain knowledge.

Customers are notoriously bad representatives for 'what to do', per "my customers would have asked for a faster horse". And they also hate being used as QA; most quality issues (which can be reliability, UX, latency, etc) need to be addressed before the customer sees it and forms their durable impression of the software.

And then also it's as you say, customers do need help from domain experts (whether they admit it or not).

> "someone needs to say if it's been done"

If that's the end user, they're not happy. End users generally don't like doing unpaid involuntary QA work.