The C++ design is optimised for the case where you're mostly storing Things everywhere and then at runtime code works out whether each particular Thing is a Customer, or a Product, or a Target, or an Artist, or what...

I don't think even an LLM writes software like this, maybe somebody's Java 101 class teaches this, but frankly I think that's a bad way to teach even Java.

The Rust approach optimises for cases where Customers and Products and Targets and Artists are stored and treated separately and if we do need the generic Thing somewhere it's pretty rare so we store the extra information only where needed.