> If this were true, you wouldn't need a REST API. I don't understand what you're trying to say here. When you make a REST call to get data, you instantly have two different sets of state: the client and the server. It's no different from SSR, it's just transmitted in a different data format (json vs html).
SSR means you don't have a clear representation of the client-side state (as distinct from the presentation) - by definition you render on the server and only serve the view layer to the client, whereas your data model only lives on the server. There will naturally be state in the client (e.g. form inputs), but you don't have a good representation of that in your model.
> You do the exact same thing with SSR. Stateless shared nothing app tier instances. Been doing it for 15 years now.
OK so where does the UI state live - not the long-term persistent entities, but things like unvalidated form input, which tab is enabled, which step of an in-progress wizard the user is on? Either you manage that on the client (at which point you're halfway to an SPA, and getting the worst of both worlds), or you manage it in the application layer on the server (in which case you have all the scaling issues), or you make every UI change go all the way into the data layer which has even bigger performance issues.