Of course this is all pending a 3rd party topo app. But this is only a matter of time. And it presumes good accuracy.
As for waterproof, Garmin will always have the edge. That said, phones are built to be more weather resistant than many other electronics, since they tend to be used and abused more. For example, many phones cover their circuitry with a laminate to protect the circuitry from short-circuiting, so that they stand a better change of working again when left to dry.
For a phone, though, the iPhone seems as about as rugged as one can get without being 'ruggedized,' with a metal frame, optical glass face, very few buttons and no moving parts. I personally would feel comfortable with an iPhone in a good silicone case inside an Aloksak.