The thing is, though, that Typescript is not solving runtime type checks. Typescript is declarative, it does not check at runtime and if you have any code interacting with third-party data sources and you do not check there, things will explode down the line.
I half agree with your response. It's true that third-party data sources need to be validated using runtime type checks, whether in explicit custom code or through some schema validator framework. But TypeScript is very helpful in the common case where the caller is fully typed, so the callee doesn't need to do all the needless defensive checking.
