Everyone love's a skeptic :)

If you properly build a large codebase using patterns like Clean Architecture, then tools like Next.js or Blitz should be fully isolated away from your app logic.

If you need auth in Next.js, your options are Blitz Auth or Next Auth. Try both and see which you like best.

If you need type safe client/server communication, Blitz RPC is one of the options.

Neither of these dictate absolute control over your code as your comment implies.