Namely view code (HTML/CSS/JS) was harder to compose in a scalable fashion, Rails'/Django's template composition feels vastly inferior to proper componentization. Namely limited type checking, globals sharing, ... These things do make it harder to refactor and get rid of unused code, which also has real impact on users.
Another biggie was that there is no great gradual path from server-code to client-code, with potentially additional data. Now React SSR does make you work more for the server use case, in that you tend to write code which should also work on the client-side (which might change with React Server Components) but at least you don't have to face lots of decisions when expanding the interactivity of your app.
All that said, I also agree with the blog that there is still lots of refinements to be done on the React side of the world, I just view the world we came from as far less rosy.