I've been wondering about when to use something like a SPA and when to use something like Rails recently. My understanding is that the two are getting closer, w

I've been wondering about when to use something like a SPA and when to use something like Rails recently. My understanding is that the two are getting closer, with React getting stuff like Next with server-side rendering, backend functions and stuff like that, while Rails is getting Hotwire to make richer interfaces easier. My question is, how do you know when to choose which one? For example, I'm looking to build something that's in the "unbundling Excel" vein. The application will have lots of input from the users, and lots of graphs. It's supposed to be pretty interactive (once again to mimick Excel). And I'd like to build a SaaS out of it. What would you pick, and why? From what I understand a SPA would be better at the "heavy user interactions" part, and a regular MVC framework would be better at everything else. Maybe a combination of the two? But with limited development times, it seems like it would be slower to do that.