Earlier quoted context omitted.
Can you elaborate more? What do other languages have over std::variant/visit?
That would be like explaining C++ Concepts to an assembly programmer from the 60s that had never used a "function" as a way of abstracting code. If you really want to know, spend one afternoon learning any programming language with built in support for that (Rust, Ocaml, Haskell, ...). ADTs is one of the first things one learns. In Rust, the features you'd need to learn are enums, patterns, and pattern matching. But…
It's not at all helpful to say that there's something so complicated on these other languages that you can't possibly get the idea across without using them.