My point is that you literally cannot SSR your client js views without a js backend, so node has a clear engineering purpose in this respect. Yes, you can import a second backend into your main backend to avoid writing node, and that's fine, maybe your team is mostly made of rubyists or maybe your existing code base is ruby, there's nothing wrong with this approach, but it is more complication and layers of abstraction than just using a js backend if you must build an SPA.