Hey! It is really a pleasure and honor to have your feedback.
As far as the technicalities go, the summary is contained in the wiki at
https://wiki.openstreetmap.org/wiki/Climbing
I've seen quite a few threads, some older than 10 years, where these issues are discussed. Then they have been summarized on the wiki page. I've also initiated a few discussions at the end of the last year.
I find having crags on a map quite useful. Whether it is practical to have every route or not, is a separate story. You are right in that the routes are (mostly) vertical. That's why route_bottom is mostly used. Easy multi-pitches can easily be as horizontal as they are vertical. But nevermind.
As OSM is just a database, projects like Open Climbing are utilizing it in creative ways to also contain photos and topos. I really like and appreciate the effort. I do like to have multi-pitch routes shown. Sometimes I add them as a crag, so they are visible within an area. Still no precise definition in that regard. I guess, in OSM things just evolve and are rarely established.
We've had tons of discussions about the categorization of Paths, over several months, with nothing coming out of it.
Even if not used, I think it does not harm to have this information on a map. There's a lot of information that I find less useful than climbing routes so I would not worry about that too much. Climbing routes don't change that often. Or at least not as often as kebab kiosks.
I believe it generally helps make the sport more accessible and popular. Which should also result in more people getting the actual guides to get full topos of the routes (or use sites like Bergsteigen). Seeing a climbing crag on a map would give one an idea that climbing in that region is possible, eventually prompting them to look for more information (I'm definitely in that group, for example). 
In any case, I'll follow you on OSM as I would definitely like to climb some routes in the Hochschwab area this year. So far I've only done some scrambling on Ebenstein and Feistringturm.