I was thinking of a lot of cases where RC is being used as a general solution for lifetime management with automatic refcounting; but most objects have a well-known lifetime with their refcount being 1 95% of the time. And another 4% have their refcount bump up to 2 briefly when they're temporarily shared, or transferred to a new owner (think returning a shared_ptr<>).

But, yeah, the "genuinely shared" case - either the 1% in the scenario above, or when RC is only being used for objects with complex lifetimes - is definitely a significant use-case I overlooked.