Another con of GraphQL (and probably GRPC) is caching. You basically get it for free with REST.

REST can also return protobufs, with content type application/x-protobuf. Heck, it can return any Content-Type. It doesn't have to be confined to JSON.

GRPC needs to support the language you're using. It does support a lot of the popular languages now. But most languages have some sort of http server or client to handle REST.

What popular languages aren't supported by GRPC?

Scala, Swift, Rust, C, etc. I guess with Scala you can probably use the Java one. But they have one for Kotlin...