> In most SPA, state is distributed with two copies floating around.

In all client-server systems, state is distributed with "two copies floating around". The difference between SSR and REST+SPA is that in the SSR, your server code is creating the markup to make it presentable to an end-user, but it's still fundamentally a copy of the state that exists on the server, and it's not obvious why the transformation to markup rather than structured data (like JSON) is desirable on the server. If anything, with SSR you need to copy more state from the client to the server, where it doesn't really belong.