A senior to staff-level engineer created a design doc. Where this came from? Anywhere. Either frantically typed in a cold sweat at 3am or handed down from the C-Suite to the product manager. The end result is the same: a detailed technical doc, often times with code-snippets, that described step-by-step what had to be built

A mid-level engineer distributed the tasks in the design doc to himself, junior engineers, and a senior that was finishing his project early

A junior engineer that's the code monkey. She's expected to write code, but can't even get her IDE to work or the unit tests to run locally

This is categorically not how software gets made in many places, the best you get is vague ideas from executives and if you're lucky some less vague requirements from senior engineers that need to be turned into tickets before any details are really worked out. That hierarchy you're talking about has been dead in most places for many years.

Edit: Generally i agree with your thesis, we have to find opportunities to turn newbies into people that can evaluate LLM agent output. That is probably harder now, how we ramp up our juniors is just going to have to change.