Kalista is going to remain a problem until her nerfs address her problems; they have yet to do so.
The first problem, her passive, makes her effectively immune to attack speed slows because her passive is NOT dependent on movement speed. If someone is in range to apply a slow (or follow up on one), then they are close enough to auto attack and that means the slow is irrelevant. They recently made her jump speed affected by attack speed slows, but this hasn't had much effect.
Instead, I would like to see the passive reworked in such a way where her jump distance is dependent on her movement speed. This way, a Kalista player will still get the increased jump distance with different boot tiers, but it has the major benefit of allowing slows to be used against her. She would still kite opponents more effectively than any other adc (one of her intended strengths) but she wouldn't be completely immune to an entire classification of CC.
The second problem is how much power is budgeted in her W. Yes, her W. With one point in the ability, proper coordination between adc and support yields a 10% max health damage hit every 10 seconds. That is a HUGE amount of trading power that can't really be answered and is up very often at no cost to either Kalista nor her support (erm oathsworn but you get the point).
This just needs a straight nerf. I'm not even sure why its there in the first place; its a cool mechanic that gives way too big an advantage in lane.
Third is her ultimate which allows her to pull her oathsworn to her and make them invulnerable no matter what the situation previously. In professional play, it means that the support (oathsworn, im going to stop saying both now) can move around in a much more risky fashion, "overstep" and "misposition" because the enemy team cannot punish and commit cool downs due to the ultimate. Its incredibly frustrating in casual play as well; at level 6 you lose the ability to blow cool downs on the support because nothing can stop kalista from using their ultimate to save the carry.
I would like to see Kalista unable to ultimate if her support is currently under the effects of a hard cc; similar to how ekko cannot ulti back when stunned, snared, or suppressed. If their movement is disabled, Kalista ultimate should not take effect until the support has reacquired their ability to move.
If one were to look back at the Kalista nerfs, none of them have been dealing with these core issues that make her kit unfair to play against. She will continue to be strong until these things get looked at.