Why kelthuzad needs a buff
No, He is already one of the strongest mages in the game and can carry teams solo. He needs a little rework on his quest, just make the quest 50% extra damage instead of 75% but give him a 25% extra spell damage at base.Fuente
I appreciate the length and thought put into your post, but from my data Kel'thuzad's win rate at Diamond-Master in Storm League is 52.1%.
It is around 45% outside of those games, but I would attribute it to the lack of traditional team comps more than anything else. Changing him to not be so reliant on his baseline quest for a power spike would absolutely require a significant change to how he works, which, as you point out at the beginning of your post, would turn off a lot of the current people who love how he plays.