Earlier quoted context omitted.
You have a simple nodejs server that renders using react nextjs, vue nuxtjs, angular universal, or ember fastboot while using rails for your APIs.
So now you've simplified your 1 app server into 2 app servers that aren't even the same language or environment.
We as developers already offload certain tasks to separate servers. Do you use your app server to terminate TLS connections? You could; but why would you when Nginx can do a much better job of it?
You could store you application data like usernames and password in a JSON file if you really wanted to. But why would you when you can run an SQL server and use a real database?
Pick the best tool for each job. JS frameworks handle the view layer better than Rails does.