Killing the dragons to get the bones is the most time consuming? Ok sure. But it is also the necessary part. If you are after slayer xp, you kill the dragon to get it, then go get the next dragon for more xp. Lets say that in order to get the slayer xp you have to pick it up off the ground. So you want only slayer xp, you kill the dragon, grab xp, move on. You want money, kill the dragon, grab the drops move on. If you only want the slayer xp then only get the slayer xp. If you go someplace to eat, we'll say McDonalds. You go there wanting a Big Mac. So you go order a Big Mac. You don't order McNuggets, 3 small fries, and a McChicken while your there, just because your there. You get what you want and move on.