Your entire argument is predicated on building an SPA; if you don't need an SPA then you de facto do not need a frontend framework (which is what the OP is implicitly saying, do as much as possible server-side).

Now, saying that, there is something to be said for separating UI from the backend. Yes, it adds ( a great deal of) complexity compared to server-side applications, but the reactive programming model is quite powerful, and useful even if you could build the application entirely on the server.

And obviously if you do need an SPA (e.g. wrapping WebView for iOS/Android) then you don't have a choice, or if you do you'll be reinventing the wheel, poorly.