For some of the Higher level Slayer creatures you do need quest. For example you need to do Rum Deal for Cave Horrors. Another thing is what slay master you are using. If you use the lower masters like the guy in Edgeville and Zanaris, you wont get good task.
Since when has there been a lever in edgeville that brought you to the same hut in the wilderness as the Ardy lever? The lever is where the coffins are.