The slow chance in your character sheet is a global stat while the affix on your idol only counts for bow hits. Therefore it will not be added to the character sheet. The “chance to slow on bow hit” works as intended though. If you have 20% slow chance and 20% slow chance on bow hit you will have a 40% slow chance on multishot but still a 20% slow chance on dancing strike for example. Other stats like Frostbite dmg are also not in the character sheet yet but will probably be added in upcoming patches.