You're saying that grpc and protobuf are over engineered but you're happy with Spring?
gRPC and protobuf are just transport and serialization, they have nothing to do with business logic, on the other hand Spring is a heavy, bloated framework.
Most Java frameworks are complicated backed by layers of abstraction and black magic.
btw no framework does not mean you don't use any library, there are some good lib aka micro framework that have everything you need to build modern and decent api servers.
gRPC and protobuf are just transport and serialization, they have nothing to do with business logic, on the other hand Spring is a heavy, bloated framework.
Most Java frameworks are complicated backed by layers of abstraction and black magic.
btw no framework does not mean you don't use any library, there are some good lib aka micro framework that have everything you need to build modern and decent api servers.
https://github.com/go-chi/chi
https://echo.labstack.com/