Yes. Schemas are useful. What alternative do you propose? The only other option I can imagine is sending the schema along with the object, in which case you should just be using XML instead of JSON.

I guess the selling point for REST still stands -- if you don't need any of that stuff, you can set up a much simpler API for rapid prototyping.

REST is often used as a very, very limited transport model for a two-bit, buggy, incomplete and incoherent clone of SOAP, yes.

Unfortunately, neither REST nor SOAP are understood by majority of developers writing code for them (to this day, I insist that the real issue with SOAP was people using IDE code generation without ever studying how SOAP works)