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/) and Fresh (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.
If you look at the hottest trend of the "island architecture". New frameworks like Astro (https://astro.build/) and Fresh (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.