> Would you agree that Rust can never eliminate the runtime overhead of dynamic dispatch, because trait objects, at a language level, require dynamic dispatch? I would not agree: Rust programmers routinely eliminate it by sticking to the statically-dispatched areas of the language. Likewise, Swift programmers routinely avoid the runtime overhead of reference counting by using structs and not classes.

Sharing is something that is pretty necessary in programming; you are severely limited in what you can do without sharing. Trait objects are not, and are pretty rare in Rust. I often see people using enums over trait objects, and only sticking to trait objects for creating extensible APIs.

Rust provides a way of sharing that does not involve any extra runtime overhead, which gets used often. Swift does have nice optimizations to value-typeify things, but without a finer-grained distinction between the kind of sharing you want to do to hint the compiler, this will be vastly limited as compared to Rust giving an explicit choice between borrows and Rc.