If you just look at the best drops you won't get a good statistical look at the overall drops. Nechryael's best drop may not be worth much now, but it's overall drops of herb seeds, death runes, charms and rune items will net you about 250k-400k per task depending on your luck. Now on the other hand, Dark beast's Dark bow may seem well, but their overall drops barely make you break even. Even if you don't require pray, you still only make 100-250k.