Multi-threaded and/or async code can perfectly exist without shared-ptrs. And no, you don't need a shared-ptr to manage the lifetime of an object shared by two threads.
That might be true of C++, but I don't think its true in Rust. Furthermore, I don't think the performance concern is as dire as you believe - both Scylla and Redpanda, two high performance C++ databases both use shared_ptr with their async framework Seastar.
> That might be true of C++, but I don't think its true in Rust
And which was exactly my point.
> both Scylla and Redpanda, two high performance C++ databases both use shared_ptr
Such argument doesn't make sense since you will find usage of shared-ptrs in probably more or less every high performance C++ codebase out there. The secrete sauce is to know _where_ and _when_ to use it. I'm not against it but I'm definitely not in favor of language forcing me to user it when I don't need it.