How To Fix Kalista
So if you don't know what is wrong with Kalista I am going to try to make it short. Basically Riot after S4 went on this whole campaign of making champions with VERY unique kits. We got Gnar, Rek'Sai, Kindred, etc. One of these unique champions was Kalista. They made her the Swiss army knife of ADCs. She had damage and utility. Well, Riot decided that they wanted to keep the utility so they decided to take the nerfs to her damage (mainly cause ult and W got hit too). Well, fast forward and she becomes the most garbage ADC because she can't do her job as an ADC. Especially after Riot gave incentives to attack speed builds and discouraged building crit by nerfing her AA ratio (what the fuck?).
So yes, we are here now with the worst ADC because Riot took away her damage, but kept her utility. As an ADC (attack damage carry) you need damage, Kalista doesn't have damage unless fed (hell AD Janna is a menace when fed). So, HERE IS HOW TO FIX HER. Stop saying that you don't want her to be a duelist. We know that that isn't a problem and it is probably better for her thematically as well as in game. She should be a duelist. Rework her W, make it so she gets a hop speed increase when activated as well as an attack speed increase. As for her E, nerf the base damage, nerf the scaling, and make it so it deals more damage based on missing HP and shows that it can execute a target. Remove her oath sworn passive. Make her ultimate a channel that powers her up. After the channel she gains lifesteal and attack damage.
Edit: She should get a visual change post-ultimate. Something like an aura and trail left behind after moving.