This is just problem of structure. I am not convinced that there is particularly higher chance to end up with "unworkable mess" with SSR compared SPAs (of cours

This is just problem of structure. I am not convinced that there is particularly higher chance to end up with "unworkable mess" with SSR compared SPAs (of course most projects end up being a mess). If you look at the hottest trend of the "island architecture". New frameworks like Astro (https://astro.build/ https://astro.build/) and Fresh (https://fresh.deno.dev/ https://fresh.deno.dev/). They are basically what are you describing. All SSR but with dynamic parts. Seems like these "islands" by their nature are less entangled than full SPA.