I find this reaction almost disturbing. There is a very big difference between a champion being annoying to play against and being OP. Have you even played Kalista? How many games? Here's my take from around 100 Kalista games played. She is a very situational pick. Her counters absolutely destroy her and she absolutely destroys the champions she counters (usually).
Lets start from the beginning. Counterplay is a real thing that some champions have and some don't. Champions that don't have it are very binary. They either win or lose because their numbers were bigger or smaller than the opponent, and the only variance is that if the opponent of said champion had more counterplay, then there is a potential for the low counterplay champ to overcome lower numbers but not the other way around. The resulting conclusion is that these low counterplay champions should be tuned slightly weaker so that they do not become oppressive (and I am not trying to display Kalista as a low conterplay champion, as you could consider almost any AA-based champion/hypercarry in the same catagory).
That being said, what does this have to do with Kalista? Kalista doesn't have any damage steroids like most traditional ADCs, but a very strong movement steroid. What does this translate to? She has incredible potential to exploit counterplay, but her "numbers" as stated above are inherently lower than other ADCs and champions so she struggles in a lot of matchups. Kalista's success has mostly to do with champ select. That being said if you wanted to, say, nerf her in any way to "bring her in line" with the melees that she can counter, you have to do it in a way that doesn't weaken her other terrible matchups, since she just doesn't put out the damage that other hypercarries do and she doesn't have the option to sell her boots lategame like other champs because her boot tier affects jump distance and it would compromise her mobility.
Additionally, you see her success in LCS, but that has a lot to do with player coordination. SoloQ Kalista play is much harder to pull off when you are not actively talking to your support and many people in SoloQ don't even know how to lane with her properly. Most supports don't realize that they can farm for Kalista with W proc and most supports don't realize how important the W proc on champions is either. Also in the late game it is much more rare to get your W procs on champions because many supports dont AA MUCH (but I'm not saying this is true of all supports) and so even though the 20% Health damage proc on rank 5 W is quite strong, you won't get it on every champion in a fight most likely, and you probably wont get it to happen more than once per target either (even though the cooldown for another proc is 6 seconds).
I will also mention her AA range is not the issue. If you have ever played Kalista you should probably know it is not easy to maintain a "sweet spot" with hops where if she hops away, she can end up out of range and the enemy can just walk away, or if she hops too close and gets CC'd and dies instantly. Some might compare this to, say Lucian, he has the shortest AA range and he can manage, but he's a caster carry. Kalista doesn't have the ranged abilities that can compensate for a lack of AA range.
Have you ever played Kalista versus Katarina? Akali? Tristana? Pantheon? Zed? LB? The list goes on, anybody who can destroy her if she hops even an inch too close is almost impossible for Kalista to deal with. Playing a kiteable champion with counterplay is literally picking into your counter and saying that it's OP. She has tons of counters. The problem isn't that she's overpowered, it's that she is binary in terms of who she will and wont beat to an extreme.
I will say that Kalista's ult is quite powerful. And in a premade, it is worth getting a nerf, it is similar to pre-nerf Yasuo ult in that respect. But I can't tell you the number of times players will miss fire Kalista's ult in SoloQ. It happens all the time. Maybe if she sees more play in SoloQ and people know more about how to play with, as, and against her, then this ult should be scaled back a bit. Maybe a range nerf and a CD nerf, but it is also worth noting that it does no damage.
Next off, you want to cap the damage on her E on monsters? That sounds reasonable, but I will argue that she only gets to place her massive amount of stacks on a single monster when you are the one to control the objective, so it's not like it is oppressive as Nunu was as a stealing tool. It would be a fair change though, since many champions have abilities with capped damage vs monsters. Also, even if it out-damages smite with enough stacks, many people combo high single target damage with smite to secure objectives, so it's not like it's impossible to steal from Kalista. Kalista also doesn't have any easy indicator of how much damage her Rend will do, so it is very possible for a Kalista to mess up, rend early, and lose the objective...The faster your team takes it, the smaller the window for stacking as well.
Lastly I will just say that I am by no means a game designer or a member of a balance team. I am not a pro player. I am not saying that I am right, only that this is my personal opinion of a champion after my personal experience with a reasonable sample size of games. Yes, I am somewhat biased because I actually play her, but this is an honest opinion that has had a lot of thought put into it on how she fits into SoloQ meta and how she interacts with other champions.
TL;DR: Scroll back up and read about how Kalista isn't OP. Reading isn't that hard.