I don't think this is a counterpoint.

An established codebase is already the best kind of context you could give an agent. It has all the patterns baked in so the agent simply follows established patterns. Such a codebase probably contains tens to hundreds of thousands of man-hours poured into it by humans refining it to do what it does - taking into account real world feedback and constraints.

When working on something from scratch, the best an agent can do is the average of whatever is in its training set and the clarity of the text prompts.