I agree with them that in any well-written program (in any language really, not just C and C++) the ownership and lifetime constraints are not necessarily enforced by the compiler - that is, they are not expressed through types or even necessarily through code at all - but they are definitely existent in the design and behaviour of the system. If the programmer cannot explain who holds what and for how long, and therefore when it's safe to read or write particular resources, then that isn't well-written code IMO.
> I can't say I've ever seen someone manually implement Arc in C
...an Arc is literally just a shared pointer. It's in the name, Atomically Reference Counted. Reference counted resources that use atomic operations to adjust the count are a dime a dozen in C projects in my experience.
Rust did not invent the concept of a multiple-reader/single-writer lock either, e.g. the Linux kernel has the `rw_semaphore` type. I don't understand treating types like this as something arcane simply because they're given an explicit tag in Rust.