This. This has always troubled me when I was an aspiring developer/designer. Although now I am neither and am on the product management track.
The only reason I still learn to code and design is out to get a faint idea of “how stuff works”, and to better understand the people that perform these skills at a high level.
I personally feel, and agree with the point that the only time a designer should code, or a developer should design is to communicate an idea effectively.