…but Rust has changed how people view languages. It has brought focus on compile-time safety, and shown it's possible and practical. It has shown that data races can be caught at compile time. It has shown that GC vs manual memory management has a third option.
Objective-C has only existed a few decades now.
AFAIK Objective-C has lots of reference counting.
The phrase "garbage collection" has also come to be somewhat associated with tracing's specific characteristics (IMO). Manual memory management is performant and deterministic, but unsafe. Tracing garbage collection is performant and safe, but nondeterministic. Reference counting is deterministic and safe, but not as performant. If you throw Rust into the mix as a fourth option I suppose you could add a "flexible" characteristic.
Not as performant in a theoretical model with unlimited memory that all costs the same to access. ie it’s not actually faster in practice when peak memory matters and swap exists.
Rust avoids copies and occasionally proves single ownership instead of having RCs. This seems to me to be overoptimization and a waste of programmer time. Copies are fine and you don’t need to prove them away.
Rust's ownership + borrowing instead of being somewhere on the axis of performance vs correctness trade-off, has traded off generality/flexibility instead (infamous for being unfit for doubly-linked lists). Unlike ARC, it works without a run-time, and on bare allocations and stack objects too. Unlike C++, it has zero-cost slices/substrings without a risk of dangling pointers.
C++ had shown this long before Rust.
The main thing I guess is dealing with C APIs in C++. You do have to use C APIs in Rust as well though, but maybe dealing directly with plain C APIs is less common because of how annoying it is. The only way to avoid that pain is to make a Wrapper library that exposes a more idiomatic and possibly "safe" interface. C++ can wrap C APIs just as well though.
I agree with you though, C++ has been doing RAII for a while and I'm not sure why people seem to think Rust invented it. Idiomatic C++ APIs and code are just as "automatic" as Rust for the most part!
(Your literal question is a straw man: no, those aren't different, but Rust offers more.)
Unique ownership prevents leaks and double-free, and borrow checking prevents use-after-free. Borrowing is necessary to temporarily relax the exclusivity of uniquely-owned objects and access their interior. Access to interior of a unique_ptr (and shared_ptr) decays it to a reference or a bare pointer that is not managed by the smart pointer any more, and can be left dangling. Borrow checker eliminates the manual "be careful not to leave dangling pointers" part.