I totally agree a proto first approach to your types can pay back in dividends if you need to serialize over different wires.

This project admittedly was developed to solve a specific need in an existing codebase with a lot existing types.

The codebase is also mostly maintain by the backend Golang engineers. Letting them use their native type system increases adoption and buy in.

Totally - The other really nice thing about Golang "type-system" ecosystem is their native ast in the stdlib. You can do so many amazing things from there. Infact if you pledge your life to Go (which I think I have atleast for now) starting from Go and generating everything outwards is not necessarily a bad strategy.