They have same costs. And we have a wm like Thalassa, totally out of control, who can keep the enemy team unable to play for a whole fight (the new cc system was supposed to prevent this, right? Lol) and needs an obvious nerf.
Then we have another wm like Zahra, with skills that are a joke compared to other this one.
There should be some kind of balance, as I said the cost is exactly the same.