SPA and react are not the same thing. React is about components and you can use React in something like NextJS which is not a single page app but a server rend

SPA and react are not the same thing. React is about components and you can use React in something like NextJS which is not a single page app but a server rendered pages. Also, SPA itself is getting outdated concept, now most apps are hybrid of initial bundle followed by a dynamically imported modules. Finally, MVC is a pattern for web pages, the complexity in the client side because what is the being shipped to the browsers are a client side apps with their own router, render functions, state management and APIs.