Kalist is one of the most balanced champions in the game

She's way less bad than kassadin. Her AA animation is long, her dash is extremely short early in the game, it requires actually autoing you (which may be difficult if you gap closed onto her or displaced her) as opposed to just pressing R to blink away.

Basically, they are both bad if you are warwick and come at them from several units away when they can perfectly see you. However, if as Xin Zhao you sneak up and gap close over a wall, Kalista will not escape unless she can actually kill Xin. Kass will still get away.