I can't really argue with that. It's a way to get nominal types in a language that has structural typing. Even though the usage is simple, the implementation is more complicated than it should be.

If for example the language was missing builtin hashmap type, its implementation would be nasty as well.

I'm not a huge fan of typing systems, the thing I like the most in TypeScript is that you can use types as little as you want and add more only when you want it. But I don't like languages like go that intentionally lack features.