First of all i would like to say that i am a huge Kalista enthusiast(one of the 7 people in Europe that actually play the champion), i picked her in most of my ranked games and always had good results with her. I love everything about her kit and her unique impact on the game.
I like that they moved the attackspeed bonus from your oathsworn to an attackdamage bonus because now you do not feel less mobile when left alone, you just have less damage.
However i agree with what i heard from other players. Its nearly impossible to dominate the lane now, which was required to do as kalista cause your Opponent (most likely a crit/on-hit adc) would just outscale you.
But even that wouldn't have killed her.
What really killed her are the Nerfs to her Range. Kiting is just straight up impossible, the 25 Range were really making the Difference. You cant walk up to stack spears, you cant walk up to poke or to hit turrets in a siege or make use of your Passive to reliably jump out of your enemies reach in case a fight breaks out. You are just too close to the fight to not put yourself in Danger.
I dont know if the Nerf was initially caused by Kalista beeing either pick or ban in Competetive, anyway this will change it. I am sure.
It breaks my heart to say it but I can't imagine someone picking Kalista over another adc anymore. She is just too bad.