I tink the way Scarlet Delirium should be implemented to work is using a system like "Sublimation" from the Sch job abilities, Sublimation uses a system where you turn the abilitie on and a icon apears indicatin you that the abilitie is chargin up taking your hp and converting it into mp, when it reaches max mp it will change the icon indicating you it has reached its max and you turn it on using the abilitie again at will.
Scarlet Delirium could be very good by using this same method i tink, turn the abilitie on and while this as you take dmg it will charge the % at wich our dmg will be boosted, by reachin its max it will change icon indicating us it is maxed and by turning it on again it will activate for the duration granting us our boost.
By using this system also we will control when we wanna use it wich wold not be random when we have too much hate and whit the abilitie we will only generate even more and just die easier.
Anyways this are my toughs on trying to get our abilitie fixed and make it usefull and not just a wasted abilitie that we will pretty much never use or it will only be activated in moments where we will simply not be able to.