Sounds like the author wants his tools to be as fully featured as the code that will embody the resultant design. In that case I would recommend learning more code instead of relying on a proxy that will never be as flexible. The best designers I’ve worked with not only understand their own domain but the possibilities and limitations of how it will be executed, because they are also developers.
I can comment on this from my experience. I studied Computer Science, and my passion for UI development led me to switch to product design after being coding for more than 10 years. I design with code too, and I did many prototypes using different UI frameworks.
But, there are different design activities, and sadly not a single tool is adequate for all.
If you are making decisions about UI layout, visuals, or UI motion working with code may slow you down. Even if you use CSS grids and flex, there is a penalty caused by the lack of direct manipulation and the freedom to try multiple ideas quickly.
To me, the author just wants better refactoring and maintenance tools over the existing visual design tools. It's a little bit disappointing that design tools evolved in many areas, but did a regression in others. For example, more or less in 2008, Microsoft did a tool called Expression Blend. The tool, based on ideas from Bill Buxton, had the goal to maintain a continuity between mocks and the final implementation. You were able to import PSD layers and later convert them to components, or to sketch the UI flow in the tool. I never used it for anything more than simple experiments, but the idea had potential. Even Adobe did a similar project that never saw the light (it was called Adobe Thermo, then Catalyst and it died with Flex).