Talon is an all-in burst assassin
All assassins were all-in burst assassins untill reworked Evelynn was introduced.
Now assassin world is divided by 2 grooups:
- Evelynn + Rengar (he got hit just as hard as Evelynn)
- rest of assassins
Stealth shouldn't be used to run-away in teamfights, but as tool to hit your foes even harder with huge "surprise m-f*cker" on face. Now, if we'd go with your 10s stealth then she'd have to use it similar to khazix/talon = mostly for escape/chasing.
You know what? i could agree on this stealth if at least 1 of 2 options below would match:
a) it was on short cooldown. Let's say 15-20s
b) it'd reset on kill or assist (but max cd 30s)
I cold even agree for it to consume 150 mana, so she wouldn't spam her invisibility all the time.
About charm: I think you've watched too much twilight bro... Evelynn with her basic skin as sado-maso enthiusiast wouldn't be very charming. Unless it's vs Urgot (he likes that stuff).
I've read her lore looong time ago and tbh i kind of forgotten everything about it. But if you say she's vampire, then maybe go with some kind of vladimir Q proc on going out of stealth? That way it'd feel vampiric.
Like:
R - Evelynn after hitting enemy champion slows them for 1,5s and deals 15% max hp (half converts to health) with 0,3 ap ratio. Hitting minions/monsters will restore health from full damage (capped at 200 hp)
Feels nukey, thematically correct, and if it weren't R but W for example she could be even viable in new jungle.
If you want i could create Evelynn kit that'd be connection between what she used to be and what she could be without making her into wtf-is-this-pink-shit-tank tier champion