An editor's value is that missing context. They notice the undefined term in paragraph one, the step that assumes a flag you never mentioned, the ordering that only makes sense if you already know the answer. None of that is a writing problem. It is a completeness problem that only shows up under an outside reading.
This is also where design feedback comes from cheaply. A concept that cannot be explained in two sentences usually has a seam in it. Documentation is the first place an unnecessary abstraction becomes visible.
The working arrangement that produces the best result is unfashionable: the engineer owns correctness, the editor owns comprehension, and neither overrides the other. It takes one more pass than shipping the engineer's draft.
The gap between knowing something and being able to hand it to someone else is where most of the value in technical work is either captured or lost.