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.
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)
Predefined schema, generate classes from schema, interact with it via HTTP.