I never understood where the idea came from that if pages are authenticated, then SSR isn't needed. Maybe because people think the only benefit is SEO. The biggest benefit is performance. SSR is still great to have behind authenticated pages, to improve load times. eg multiple tabs, continuing sessions, etc. There are countless examples of sites that usr SSR + CSR + Auth - Netflix, Github...
The only other benifit of Next.js other than SEO is the project architecture that it provides.
If you are building web apps that live behind auth, it's a no brainer to use CSR. It's easy to deploy, cheaper to host and serve, not harder than SSR to develop. The cons about performance can be solved using code splitting. Moreover with proper caching, the app loads instantly.
Are there new age alternative CRA that provides a scalable project architecture like Next.js provides. Maybe it can come with basic libraries like react-router, react-query, pre installed and Vite pre configured.
Of course, there are tradeoffs. Code splitting might help a bit for someone with a slow connection, but I wouldn't say it "solves" the problem like truly streaming content does.
Yeah, it's like a trade off. You can't have your cake and eat it too. With CSR, you distribute the load of rendering to your clients, which reduces your cost, which in turn allows you to provide better service.
