Uncomfortable with Docker? Today? Or microservices? Or mixing Kotlin with Java?
I haven't used gRPC myself, but it looks like a strong standard. I have used Protocol Buffers in the past, though, and I certainly wouldn't be afraid of it just because I hadn't used it.
I've seen this kind of ultra-conservative outlook with Java developers fresh from enterprise jobs. Worked with one developer briefly who insisted that every new API would take at least two weeks of work. Even if the API was completely trivial CRUD. When I mentioned that I was using a framework that could stand up a new CRUD API in minutes, complete with authentication, validation, and user-based access protection, the developer called me a liar.
Which was funny because I'd just done _exactly that_ for another client, standing up the entire stack _and_ creating ~40 CRUD REST APIs (with parallel Socket.io APIs for real time updates) in about 8 hours. Adding or changing a model for one of the databases from that point forward just required a few lines of model specification code; additional custom code per-API was entirely optional. Of course I wasn't using Java Spring, so that may have been an unfair advantage, but there's a reason I don't use Java Spring...