karthus ult rework

recently spectated a friend who was playing karthus againest a nidalee jg, vald top, fizz mid, corki adc, and lux sup. his ult ended up being useless for the whole game as nid, lux, or fizz can just zhonyas and corki had heal while vlad and fizz did their invulnerable things. karthu's ult seems to be in need of a rework... maybe split the ult's dmg as half in the beginning of the channel and half in the end of the channel so if the enemy chooses to go invulnerable for the first half they must at least take the second or vice versa. or it could just be doing his ult's dmg over the duration of his channel so the enemy has to take parts of the ult's dmg.... this way karthus may become a bit more popular and less facepalming when the enemy dosent die to his ult because of zhonyas or spell shield or other invulnerable crap.