Maybe it is because I'm a bit too deep in the React ecosystem at this point, but once you start trying to do any reasonably complex task, this seems like it would be significantly harder to reason about.
Also, unless I'm misunderstanding it, this revolves a lot around the backend returning HTML to do backend-as-frontend, which given my previous experiences with the concept, I wouldn't want to touch with a 10ft pole. When you consider users with extremely bad internet connections (there are still people on dsl/older satellite/2G), having to make more requests to the backend that return larger blobs of html (as opposed to fewer requests that return JSON when it is relevant) will result in a significantly more degraded user experience
Also, unless I'm misunderstanding it, this revolves a lot around the backend returning HTML to do backend-as-frontend, which given my previous experiences with the concept, I wouldn't want to touch with a 10ft pole. When you consider users with extremely bad internet connections (there are still people on dsl/older satellite/2G), having to make more requests to the backend that return larger blobs of html (as opposed to fewer requests that return JSON when it is relevant) will result in a significantly more degraded user experience