I've been maining Kalista for a little while now. Once I got her basic mechanics down she quickly became my favorite champion and ADC. Setting up "Move/Attack on cursor" as shift+right click as a sort of panic button for kiting in hectic situations helped a lot.
I'm only a gold player, so not all of what I say should be considered in regard to high elo play.
Pre-ranked play I had an 80% winrate with her. I don't feel like she is gutted. You just really need some hard peel and a solid tank support to duo with.
If your team has no peel you're going to have a bad time. 
I find bringing tenacity runes in the yellow tree to be crucial, getting slowed feels unexplainably bad on her.
Also, I've created a Club in NA for kalista mains called "impale the cowards".
If anyone would like to join just add me.
"Spectre Spears".