Note that protocol buffers != gRPC. The reason you can't (directly) consume gRPC from a browser isn't because of protocol buffers, it's because there are no browser APIs to permit client code to work with HTTP2 streaming.
Clients consuming protocol buffers does require some tooling, but it's not that much more complicated than the tooling that is needed to consume JSON, which also requires a separate library for almost any language. Once you get past that, though, protocol buffers are relatively more language-friendly. The designers put a lot of thought into trying to ensure that it's difficult to design a protbuf-based format that can't be mapped onto the semantics of virtually any language. That is not the case with JSON, which, by being schema-on-read, makes it relatively easy to accidentally create an API that is fundamentally difficult to consume from many popular programming languages.
That isn't to say that it's perfect, but one thing I do like about the protobuf approach is that problems have a tendency to stay solved once you solve them. JSON-over-HTTP seems to always lead to this chronic low-grade messiness that seems minor at first, but the cost adds up over time.
Clients consuming protocol buffers does require some tooling, but it's not that much more complicated than the tooling that is needed to consume JSON, which also requires a separate library for almost any language. Once you get past that, though, protocol buffers are relatively more language-friendly. The designers put a lot of thought into trying to ensure that it's difficult to design a protbuf-based format that can't be mapped onto the semantics of virtually any language. That is not the case with JSON, which, by being schema-on-read, makes it relatively easy to accidentally create an API that is fundamentally difficult to consume from many popular programming languages.
That isn't to say that it's perfect, but one thing I do like about the protobuf approach is that problems have a tendency to stay solved once you solve them. JSON-over-HTTP seems to always lead to this chronic low-grade messiness that seems minor at first, but the cost adds up over time.