I see the problem but that is, surely, where the experience of the Captain comes into play. If the visual cues are not good enough for the Captain to judge if the approach and landing is viable, from either seat, then throw it away.
I hear what you are saying, and that should be the case, but unfortunately it is not always like that. In the S92 for example, 95% of the time the NHP cannot see anything of the final approach to land on a deck due to the set-up of the cockpit windows and spars etc.. It is an unfortunate design for rig landings, but it is the aircraft more and more of us use now. The customer has demanded it! If the captain was to only allow a landing when he had good visual cues then he would be the only one landing!