Granted, I expand on my quote: There are always several (competing) ways of doing things in OSM. No matter how much they break with assumptions.
I wrote: leisure=route;sport=mountaineering would capture more of subject matter. I stand to this. Two level tagging even might allow for other sports to use the same base tag, e.g. leisure=route;sport=snorkelling (was mentioned on one of those path topics as an example of what path gets used for.)
So in the envisioned relation type=route the natural=arete would be part of the relation, but split twice around the (fictional) pillar(s) or whatever reason to stray from there, and there would be short route=mountaineering stretches where the route does not follow the arete but instead passes around some obstacle?