Great for startups who dont need to worry about the codebase in 10 years. Not so for medium to large companies who are going to be stuck with a rube goldberg machine in 10 years.
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.
Should they? For small startups it might be better to skip paying the cost of such abstraction and just marry with a mature technology.