Personally....
I love playing her and have sacrificed a couple ranks to learn her in ranked. But, I'm getting there.
When thinking or speculating about her kit, and coming to some predrawn conclusion about what items must be her core, I think people are kind of sabotaging her potential in their games.
When people play her assuming that she needs her charm to actually carry, they generally do themselves more harm than good, and while they might manage a 9-11 kill game, their damage footprint is low because they just never actually engage anything unless through their conditional Q's and W's.
If you play her meta kit, I agree. She is in a rough spot. However, if you expand your mage potential, you'll find she is able to do crazy scores not only in KDA, but in overall damage (meta average damage is like 12k per game to champs), and be oppressive in a team fight by bombing away 900-1800 hp off their entire team.
I'm going to copy/paste another Evelynn post, and show what she can actually do a bit:
Okay. I just wanted to leave this here. It's not the best ELO game, but I just had my first massive damage Eve game since the rework.
[img]https://i.imgur.com/Ku4VaZS.png[/img]
I've been playing with different mage builds on her, and I've found one that actually acts like a monster. I got my E's up to 1400+ a hit, and R up to 918-1836.
And no. It didn't need a proto belt, even vs an Ezreal, Vayne, Anivia. My move speed was enough to make it work, and I was 2 sec shredding farm (notice the 180 cs on a champ that normally has trouble getting 60-80 without impeding her gameplay)
I'm not saying this is normal performance, but it shows that when she's a monster, she can be a monster.
P.S. I pretty much never charmed after 16 minutes or so. I just dived with E, Q spammed, and Ulted when the other team grouped and was about to cc (hence the only 13 kills). You'll notice only 9 Crowd controls (9 charms).