Yeah that shortcut is relying on a mechanic that I didn't really showcase here, still not sure how to do it in game. Let's say it might be easier to get there the other way around! :)
As for the crossbow it's indeed not required, it's just a way to go through alternative paths. I could say it's all carefully planned, but yeah it's to easy to lose the bolt and didn't have time for a solution to this :D