I haven't used CRDs myself for a few years now (probably since 2021), but I still remember developing CRDs was an ugly and hairy experience to say the least, partly due to the flaws of Golang itself (e.g. no traits like in Rust, no macros, no enums, etc...). With protobuf you can easily compile your definitions to any language with clear enum, oneof implementations, you can use the standard protobuf libraries to do deepCopy, merge, etc... for you and you can also add basic validations in the protobuf definitions and so on. gRPC/protobuf will basically allow you to develop k8s controllers very easily in any language.