You don’t re render a template. Only what you need to. If it’s a single div then so be it. Which is why it’s SPA-like experience with server side code
Again, this is a different spin on doing things. Rails preaches abandoning the over-complexity of the client-side in the browser and pushing work to the server.
I personally love it. I'm sure someone who is as fast in React as I am in Rails is laughing reading this.