I will try and explain Riots clever logic behind balancing champions:
Step 1: Create a stupid broken and toxic champion, maybe overpowered if you like.
Step 2: Wait until the community is sated with hate against that champion.
Step 3: Nerf all things of that champion except for the things that are hated so that the champion gets horrendously weak and underpicked.
Step 4: Finally address the actual problem using a rework or nerf while compensating the champion with a lot of nerfs.
Step 5: Watch the mains of that champion cry.
Rinse and repeat.
Note that Kalista is currently in Step 3.
Edit: Yasuo has just finished (or rather has been finished by) Step 3 and i still waiting for Step 4 to remove one of his passives, his W, endless dashing and "synergy" with the likes of Vi and Malphite. Same for Poppy (who is being worked on),
Veigar and Kassadin are already through the whole cycle while Zilean skipped Step 3.