I feel so sorry for Dodu, he post legitimate explanations and no one can seem to just listen and understand.
When you do any action you have CE (Constant emnity) and VE (Volatile emnity), Decoy transfers your CE which as the word constant makes it sound is a lower building, never reducing single number. However VE Which the word Volatile imply's is Rapidly building, but decays over time.
When you go test this ability with no knowledge of CE / VE numbers of every single action done in the span of the fight you will never actually know why you don't pull hate.
Decoy shot is nothing but helpful, don't use it at the start of the fight with 300% tp then come on here and tell people it doesn't work for WS or Barrage Ect. Tanks do not need 5 mins to build hate, In fact a Nin/Drk now-adays can cap hate in 48secs with full buffs but sadly Nin/Drk is pretty useless when you could just DD the mob.