As an example Genatron is made possible by fine-tuning in order to create entire applications that are valid. It's similar to the valid json example, where you want to teach specific concepts through examples to ensure the correct syntactic and semantic outputs.
It has been full circle indeed. React is great for front-end development but with the need for having some pre-rendering (e.g. SEO) it's understandable why server-side re-entered the picture. However, with Next it has been slower build times and various twists and turns (a lot of the same things PHP was always bashed for). That's why for SPA apps we now default to Vite + react-router for a 10x speed up in build times on the same hardware.