Obviously modern harnesses have better features but I wouldn't say it invalidates the mental model. Simpler agents aren't that far behind in performance if the underlying model is the same, including very minimal ones with basic tools.

I'd say it's similar to how a "make your own relational DB" article might feature a basic B-tree with merge-joins. Yeah, obviously real engines have sophisticated planners, multiple join methods, bloom filters, etc., but the underlying mental model is still accurate.