Kalista Balance Suggestions
What I am going to do is emphasize Kalista's strenghs as an early to mid game lane bully marksman and reduce her late game scaling so she can have an obvious weakness where she is strong early, but falls off late game. I would not consider my changes to be either nerfs nor buffs, but considering Kalista is on the strong side (still mechanically sound, so you should not see her in low tier play, or rarely in mid tier play even).
Martial Poise (Passive): Hop now scales based on current movement speed minus 75 from 250/300/350 based on base, tier 1 boots, and tier 2 boots.
What this means is that you still get 250 units per hop with your base movement speed, but a lot of movement speed can me you get a hop range buff BUT slows can now effect Kalista'a hop range. Ghostblade and Talisman can give super hops, and Ashe and Rylais will grant sluggish hops; so it is a nerf and buff - meaning it is a buff that grants more tools of counter play which this grants a nerf as well in this aspect.
Pierce (Q): Damage changed to 90/180/270/360/450(+0%AD) from 10/70/130/190/250(+100%AD)
This change removes the ratio and increases the base damage; it allows the spell to be big damage early to mid game, and falls off late game. Buff below 200 AD, and a nerf above 200 AD.
Sentinel (W): Passive buddy-buddy damage changed to 80/160/240/320/400 bonus magic damage from 10/12.5/15/17.5/20% of the target's maximum health
The coolest thing about this change is that it rewards the duo-lane working together better in the early game, so flat damage means stronger early to mid and weaker late game than % max health. This makes Kalista even weaker with trying to kill tanks, but she can try to kite them and kill them that way with Rend stacks built up.