I'm gonna compare 2 abilities (for utility sake)
Xin xhao's crescent sweep (R) to evelynn's agony's embrace (R)
both deal % current hp damage 15% for crescent sweep compared to 25% for agony's embrace both are AOE, One is magic agony's embrace whilst the other is physical. crescent sweeps's cooldown is 120/110/100 compared to 150/120/90 (cresent sweep's cooldown is also lowered significantly by q) agony's embrace has a slow while crescent sweep has a knockback AND as of recently a 0.75 second stun crescent sweep gives 15/20/25 armor and mr per champion hit 75/100/125 for 5 champs agony's embrace gives a shield of 150/225/300 per target hit 750/1125/1500 for 5 champs crescent sweep deals a minimum of 75/175/275 (100% bonus AD) agony's embrace deals a minimum of 0 damage but also has a low and meaning less ratio of an additional 1%hp per 100ap.
who has more burst in their whole kit? Xin-zhao who has more cc? Xin-zhao who has better ganks? Xin-Zhao
Summary: Buff that Awful cooldown on agony's embrace and give it some get rid of that useless ap ratio and put a base damage.