I think you’re both mostly on the same page. In order to route through an area without relying on an explicitly mapped linear feature, some postprocessing has to happen. The proposed relation members sound like a hint to prioritize some visibility paths over others, but not quite a replacement for this postprocessing. The question is who needs to do the postprocessing.
It sounds like the proposal here is for the OSM API or the planet generation process to postprocess the geometries or the relation-based hints instead of leaving it to individual data consumers to implement. I’ve heard that many OpenTripPlanner instances even disable the visibility graph functionality because it’s resource-intensive. Centralizing that effort in the distribution could make sense if we consider it an essential step for making sense of the data.
I’d look at how the ecosystem is currently coping with the need to postprocess coastlines and lakelines, which are essential in cartography and also less than straightforward.