Well, the main reason I find that advice valuable is that a beginner has no way to know what to design.
(Other than if he reads a spoon feeding book at the very beginning, which I think is more harmful.)
I think your perspective is a little bit skewed on this because of your experience in designing stuff from scratch.
For example, just a few days ago, I was very puzzled about how to design a scene like hierarchy of objects.
The first time everything clicked into place is *after* I managed to write some ugly and unstructured code about using "assimp" to import a scene from .blend files.
After that the design went comparatively smoothly.
>you will ultimately and only be trying to reuse code
I agree that would be dangerous, but have avoided doing that more than once.
>you only learn that you need a camera system, but to actually refine a camera system, one must exist.
Exactly my point and the same one made by the article.
If you try to make a 'well designed' camera system without knowing how view matrices work, it would be a rather unusual camera. :P
Designing and learning computer graphics at the same time doesn't work very well for me, so I have successfully managed to break the process into interleaved pieces.