The problem is, protobuf isn't just a serialization protocol, it's also a bunch of generated model code you have to start using in your application. You don't just serialize your domain model to protobuf, you tell protoc to build you some classes that become your model.

Which means if you aren't careful, you can't easily move to anything else for serialization, ever again. Your code now uses protobuf-specific objects everywhere, because that's what protobuf encourages. I'm currently in a codebase where countless method signatures (which should be serialization-agnostic) take or return `Message`-derived objects because, that's what we get when we read in a request or emit a response, and using those types everywhere was just so tempting.

And now, we have new requirements that introduce some dynamism to our data model, in a way protobuf doesn't provide, so we're trying to move away from protobuf, and it's turning out to require a rewrite of practically everything because these protobuf classes are our data model, so everything depends on them.

What I've come to prefer is for serialization to be implemented a the boundaries of your service, with your models at least somewhat isolated from any given serialization technique. Protobuf is a foot-gun here because it blends these roles in a way that's hard to get away from.