Crona was always a powerful foe, but after he merged more and more with his sword and the black blood his abilities really got strong. Then he even got to merge with the ultimate evil and attained a new level of power. At that point his abilities are even higher than Ayato’s. Ayato has his demon control and in his winged form has great amounts of strength and durability. His greatest asset is likely his regenerative abilities, but that will only buy him some time. Crona wins.