I think there are legitimate criticisms of Rust that fall in this category, but the orphan rule ain’t it.

In most other languages, it is simply not possible to “add” an interface to a class you don’t own. Rust let’s you do that if you own either the type or or the interface. That’s strictly more permissive than the competition.

The reasons those other languages have for not letting you add your interface to foreign types, or extend them with new members, are exactly the same reasons that Rust has the orphan rule.