This is not true with something like Turbo: the partial transfer may or may not take place depending on whether it's useful to do that. The point is that you don't have to even care about that (and I'm not even sure you even any control over that). From the perspective of a Rails programmer, you're generating whole pages. How they get to the client is immaterial to you. Think of it as compression (which is actually is, basically using the previously tranferred data as a dictionary).
It's alright, Rails programmers can do that. Nice little trick for building SPAs. There are other systems that use the technique, it has some advantages and disadvantages. If it works for you, great. What's the point to argue against the advantages of SPA?
That's SPA fetching HTML instead of JSON or something. You are welcome.