Zoe does too much damage relative to her gold
Here's a screenshot. Zoe had the least amount of gold in this game (except for one of the two supports) but had 3rd highest damage. 3.8 CS per minute - only 133 in a 35 minute long game and only 4 kills.
Yet she still had more damage than Orianna despite having less gold and less items than Orianna - and Ori actually participated in more kills.
Edit: Imagine if an ADC had the 3rd highest damage in the game, but had the 2nd lowest gold in the game. A carry is supposed to need gold in order to carry. Zoe doesn't need gold in order to do her job.
https://i.gyazo.com/thumb/1200/ca6419eb7760303e03e1bfcad1a3348a-png.jpg
's a squishy and immobile mage. I personally have a disdain for burst damage in general, but her primary damage is on a difficult-to-hit easy-to-read skillshot. If you get hit by one while you're not CCd and have her in vision, it's usually your fault. The reason she doesn't have much gold and did a lot of damage is probably because she was focusing on poking/killing enemies over getting CS.