Problem is she's way too squishy. She has the least base HP of all AP assassins except Leblanc(if she's even an assassin anymore) and all of them deal damage upfront whereas Eve can't. That and she has trouble getting to anyone to get her combo off. She needs that charm to do anything and she has to wait 2.5 seconds to get it.
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Yes, actually, assassinating low health champions is what she's good for. That's what she's always been good for. Which makes her a situational pick. You shouldn't pick her into games where the enemy has lots of heals and tanks and CC. Like, duh.
Pick her into a game where the enemy has little sustain, with some artillery or good poke on your team, so their healths will get low frequently, and where they're kind of squishy and even better if they're weak in hard CC, and your Eve will shine. She's a situational pick, always has been.
You can't actually get to someone to kill them to do anything. Eve doesn't shine in anything because there's no way for her to actually get to her target, and her target has way too much time to react to where it's instead Evelynn that can't react instead of her enemy. 9/10 wins Evelynn will get carried, the other times she got lucky and is playing against braindead enemies.