(What is behind the Suggestion)
I started playing the game recently, and chose Classic Mode because i wanted to play for the long run. My starting strategy was Leveling both Ranged, Magic and Defence, so i would have 2 attack styles level'd up in little time, and be able to skip Attack and Strength for a while. While leveling up those 3 skills i did a little bit of Slayer and ended up getting 55 Slayer part of the plan to get a Slayer Staff.
I usually used this setup in small xp rate servers since it is pretty good (damage) and can be achieved with 5-10hours of gameplay (without needing Attack right at the start), pretty much a skill i wouldn't have to worry for a while.
Turns out when i equipped the Slayer Staff, i found this spell book:
(TL;DR: The Slayer Staff, doesn't even have Slayer Dart on the spell book).
Current Slayer Staff Spellbook
This spell book doesn't really make sense, people work for Slayer Staff so they can use the Slayer Dart spell, it is a good 55-75 Staff in general (one of the main staves/spell for common use of people grinding Classic Mode).
(Example)
of a
Slayer Staff Spell Book
(This spellbook is missing the new Wrath spells but that's not my point), my point is that this one has the main spell that makes people wear the staff in the first place the Slayer Dart.
To make it clear, my suggestion isn't to add the second spell book, the suggestion is to re-arrange the current one, adding the Slayer Dart spell to it.
Thank you for the attention, make sure you reply if you agree that the Slayer Staff requires the Slayer Dart as a auto cast spell.