RC is not deterministic. That's the whole thing - when you free a refcounted object, you do not deterministically know how long is it going to take, and on systems that try to avoid RC-induced pauses, you don't get to know when the memory is going to be released.

If you want to talk determinism, you need to actually invest into deterministic behaviour - something that either requires dropping dynamic memory allocation altogether, or tends to go for GC with known determinism guarantees (for example, IBM Metronome).