I agree, this is a real benefit of RAII compared to defer. That said, there are disadvantages of making the resource freeing part invisible.

RAII doesn't make resource freeing invisible. It makes it obvious, deterministic, and predictable. The runtime guarantees that, barring an abnormal program termination that's not handled well, your resource deallocation will take place. This behavior is not optional, or requires specifying ad-hoc blocks or sections.