This problem definitely exists in C++ or Rust.

The solution in those languages is either to use something like serde validator, garde (for Rust), or go all the way to protobufs... or write your own data validation/parsing by hand.

Rust and C++ don't even have a Javascript deserializer.

Agree with you on it being the fault of the ecosystem. But, Zod is pretty good for parsing (rather than validating). It is IMO what makes TS (or should I say Zodscript) very successful