riot tried making an assassin do sustain damage while bringing cc, which caused two problems
sustained damage champs are tanks, which have tank to survive in order to do the damage, or adc's which have range for safety
ekko had melee range, and if he built assassin glass cannon, he could be turned on and killed before his damage did anything.
Ekko needed tank
cc on an assassin... there is a reason why silence was removed from every assassin in the game, it was not fair or balanced, same with a champion that can bring so much cc, adding tank to it meant he coulg survive, deal the sustained damage, kill things, and have the ult as a fallback, or damage, and you have to kill him twice.
tank ekko was just a bomb that was soon or a later going to occur