JS __is__ dumb at handling binary. The overhead is significant. The first thing to do when optimizing a Nodejs program is always replace loops that iterate through individual byte of binary with some native(wasm?) equivalent. JSON on the other hand isn't affected by this overhead. Because JSON.parse is a native method on every platform.

I once doing a mixing of two buffers that contains PCM. A simple task that take two number, average and put into another buffer. The native implementation is about 10x fast than the one I wrote with JS (Or consume 10X less cpu time).

A native Protobuf is definitely going to beat a native JSON implementation. A JS Protobuf if also likely to beat a JS JSON implementation.

But a JS Protobuf to native JSON? I doubt.